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Triaxial compression tests on an undisturbed sensitive clay Hirst, Terence John 1966

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TRIAXIAL COMPRESSION TESTS ON AN UNDISTURBED SENSITIVE CLAY by TERENCE JOHN HIRST B o A o S c p University of British Columbia9 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied Science in the Department of C i v i l Engineering We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA MAYe 1966 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r -m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s * I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i -c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . TERENCE JOHN HIRST Department o f C I V I L ENSINEERING  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date MAY 1966 ABSTRACT An experimental investigation into the st r e s s - s t r a i n behavior of an undisturbed sensitive clay i s presented 0 The st r e s s - s t r a i n characteristics of both drained and undrained t r i a x i a l tests are considered., The drained and undrained shear strengths are compared for both the maximum p r i n c i p a l stress difference and the maximum eff e c t i v e p r i n c i p a l stress r a t i o f a i l u r e c r i t e r i a . An attempt i s made to correlate the drained and undrained shear strength through the use of energy equations which account for volume change. The magnitude of pore pressures that develop during drained tests i s estimated„ and a br i e f discussion of the effect of rate of s t r a i n on the behavior of the clay i s also included. The s o i l tested was a sensitive laminated s i l t y - c l a y of marine o r i g i n . The experimental work consisted of standard s t r a i n -controlled t r i a x i a l compression tests performed on saturated, nor-mally consolidated, 2,8 i n s , by 1,4 i n s , diameter samples. The s t r a i n rate i n both the drained and undrained tests was 0,5 percent per hour,, except for one drained test sheared at 2,5 percent per hour. A l l consolidation and drained shear was conducted under a back pressure of 10 lbs,/sq, i n . Drainage was permitted from both ends of the sample 8 but no f i l t e r paper side drains were used. Pore pressures were measured at the base of the sample using a Bishop and Henkel n u l l - i n d i c a t o r . The samples were sheared u n t i l approxi-mately 30 percent a x i a l s t r a i n had been developed or u n t i l f a i l u r e had occurred, A discussion of the testing procedures i s included. The results of the investigation indicated that the s e n s i t i v i t y of the c l a y i s of primary importance i n determining the behavior of s o i l under l o a d , A r e l a t i o n s h i p between v o i d r a t i o and s t r e n g t h that i s independent of s t r e s s path does not e x i s t i n undistrubed s e n s i t i v e c l a y s , nor does there appear to be a common d r a i n e d and undrained s t r e n g t h envelope at the maximum p r i n c i p a l s t r e s s d i f f e r e n c e f a i l u r e c r i t e r i o n . A p p l i c a t i o n of the Bishop and Rowe energy c o r r e c t i o n s to the d r a i n e d s t r e n g t h obtained at the maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o d i d not y i e l d the same e f f e c t i v e s t r e n g t h envelope as that determined from undrained t e s t s at the same f a i l u r e c r i t e r i o n , but the value of M (the s lope of the q W~P* curve) i n the Roscoe, S c h o f i e l d , and T h u r a i r a j a h energy equation was approximately c o n s t a n t 0 The uncorrected e f f e c t i v e angle of s h e a r i n g r e s i s t a n c e , 0% was found to be a f u n c t i o n of f a i l u r e c r i t e r i o n and drainage c o n d i t i o n . The s t r a i n at which f a i l u r e occurred i n d r a i n e d t e s t s , although decreasing with i n c r e a s e i n c o n s o l i d a t i o n s t r e s s , was l a r g e , i n d i c a t i n g that the g e n e r a l l y accepted f a i l u r e c r i t e r i a of maximum p r i n c i p a l s t r e s s d i f f e r e n c e and maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o are not s a t i s f a c t o r y f o r s e n s i t i v e c l a y . Although c a l c u l a t i o n s showed that pore pressures were developed at low s t r a i n s i n drained t e s t s , i n c r e a s i n g the r a t e of s t r a i n from 0,5 percent per hour to 2,5 percent per hour d i d not n o t i c e a b l y a f f e c t the s t r e n g t h or s t r e s s - s t r a i n behavior of the 2,8 ins„ by i 0 4 i n s 0 diameter sampl iv CHAPTER 1 1.1 1.2 CHAPTER 2 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9 2,10 CHAPTER 3 3,1 3,2 3,3 3,4 3,5 TABLE OF CONTENTS INTRODUCTION*) o o o o o o o o o o o o o o o o o o-o. o o o o o o o o o o o o o o Pllirp08£ 0 0 0 0 O O O O O O O O O O O O O O ' O O O O O O O O O O O O O O O O O O O O O S C O p & O O O O O O O O O O O O O O O O O O O H O O O O e O O O D D f i O O O O O O O O O DESCRIPTION OF SOIL TESTED AND TESTING P R O C E D U R E S , 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 0 0 0 0 . 0 0 , 0 0 0 Description of soil 0 0„ 0 0 Sampling and sto r i n g , , 0 . Preliminary t e s t s 0 0 0 , 0 0 0 0 , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Preliminary c o n s i d e r a t i o n s , , 0 0 0 0 0 0 , 0 , 0 0 0 0 0 0 0 0 Description and preparation of equipment,0.0. Test preparation, sample trimming and placing. Application of chamber pressure, sample saturation and i n i t i a l c o n s o l i d a t i o n 0 0 0 0 0 0 0 0 0 0 Drained shear t e s t s o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Undrained shear t e s t S o 0 o~s 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Back-drainage, dismantling and cleaning,„ 00.0, I 0 0 O O O O 0 O O O 0 0 O O O O 0 0 O O O I O O O O O O O O O O O O Q O O O O O O O O O O O O O O O O O O O O O O DISCUSSION OF TESTING PROCEDURES,, IntTOdUCtion 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sampling$ waxing 9 and s t o r i n g 0 o o o o o o o o o o o o o o o o Sample p r e p a i r e t i o n o o o o o o o o o o o o o o o o o o o o o o o o o o o o Water content and volume measurementse 0 o 0 0 o o o 0 TeSt equipment o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o PAGE 1 1 2 4 4 8 8 11 12 16 18 19 19 21 22 22 22 22 23 24 V PAGE CHAPTER 4 DISCUSSION OF TEST RESULTS, a„»o•>„o»oo«o»ooo,o 31 4 o l I n t r o d u c t i o n , O O O O O O 0 O O O O C O O O O O O , O O O O O O O O O O O O 0 31 4,2 Sensitivity and'Structure, Oooooo,oooooooo,ooo 33 4 0 3 Residual pore pressures developed during drained shear t e s t s , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 0 34 4 0 4 Energy c o r r e c t i o n s 0 o 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 42 4 0 5 Stress—strain r e l a t i o n s h i p s 0 0 0 0 , 0 0 0 0 0 0 0 0 0 0 0 0 0 53 4 0 6 Shear s t r e n g t h o 0 0 0 0 0 0 0 0 0 0 0 0 0 » 0 0 0 0 0 0 0 o 0 0 0 0 0 0 0 0 61 4 0 7 S u n u n a r y , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 76 CHAPTER 5 C O N C L U S I O N S 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 0 0 77 CHAPTER 6 SUGGESTIONS FOR FURTHER R E S E A R C H , „ 0 0 0 0 0 0 . 0 « 0 0 79 NOMENCLATURES 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b o o o o o o o o o o o o o o o o o o o o o o o 82 LIST OF R E F E R E N C E S 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 84 A P P E N D I X 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 87 LIST OF TABLES P h y s i c a l p r o p e r t i e s of Haney clay„ „ 0 0 0 «<, « Chemical p r o p e r t i e s of Haney c l a y , , o o o o o » Water contents of s i d e trimmings compared to the water content of the whole sample. Summary of t e s t r e s u l t s o o i o t t i o i o o i i o i H v i i LIST OF FIGURES FIGURE P A G E 1 „ Grain size distribution of Haney clay, „ 0a »,,,,,o , o 0 , « , . 6 2 , Typical standard consolidation curve for Haney clay,,.. 7 3o Sampling the c l a y , o o o o o o o o o o o o o . o o o o o o o o o o o o o o o o o o , , , , , 1C 4 , T r i a x i a l c e l l and chamber pressure s y s t e m , , , , , 1 3 5 , Drainage and pore pressure.measuring system,,,,,,,,,,,, 14 6a T r i a x i a l . e q u i p m e n t ! 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 Trimming tools and prepared s a m p l e 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 17 8 0 Sample in place on t r i a x i a l b a s e 0 0 0 0 0 0 © 0 o 0 0 0 0 0 0 © 0 0 0 o 0 o 0 17 9o Sample during shear e o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 20 1 0 , Relationship between coefficient of consolidation and mean effective stresso 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 38 110 Relationship between computed pore pressure and axial strain in a drained t e s t o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o ^0 1 2 , Showing the effect of computed pore pressure on the effective principal stress ratio in a drained test,,,,, 4 1 1 3 , Relationship, between water content and mean effective stress for t r i a x i a l consolidation,and unloading (back-drainage) , 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 , 47 1 4 , Application of the Rowe energy correction to test S - 1 7 , , 4 9 1 5 , Application of the Roscoej Schofield and Thurairajah energy correction to drained and undrained test data,,,, 5 1 1 6 , Stress-strain curves for test S - 1 7 o , o o , o o o o o o , o o o o , , o , , , 54 1 7 , Stress—strain curves for test S — 1 6 0 0 o , , o , , o o o o o o o , o , o o , , 55 1 8 , Stress-strain curves for test S - 1 5 , , 0 o o o o o o o o , o o o o o , , , , . 5 6 v i i i PAGE 19o Load-deformation curves f o r rubber and Haney clay 0 ooo*oo 58 20e S t r e s s — s t r a i n curves f o r t e s t S—lOooo'ooo'ooooooooooooooo 59 2 1 0 S t r e s s — s t r a i n c u r v e s . f o r t e s t C—U—10 a oo o o o o o o <> o o o oo o oo o 62 22o S t r e s s — s t r a i n curves f o r t e s t C—U—5 0ooooooooooooooooooo 63 23o S t r e s s - s t r a i n curves, f o r t e s t C - U » 7 0 o o o o o o o o o o o o o o o o o o o 64 24o R e l a t i o n s h i p b e t w e e n . n a t u r a l - s e n s i t i v i t y and degree of m o b i l i z a t i o n of <j>' at ( c i ' - 0 3 s ) maXo , 0 0 0 0 0 0 0 0 0 0 0 0 0 65 2 5 0 Uncorrected maximum p r i n c i p a l s t r e s s d i f f e r e n c e f a i l u r e , e n v e l o p e s 6 0 0 0 0 0 0 0 0 b o 0 0 < r o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 a 0 0 0 0 0 67 26 o Uncorrected maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o f a i l u r e envelopes00ooooooo-ooooooooooooooooboooooooooooo' 67 270 C o r r e c t e d maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o f a i l u r e e n v e l o p e s 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 67 28o R e l a t i o n s h i p between water content and a x i a l s t r a i n i n a d r a i n e d t e s t o 0 0 o o o 0 0 0 0 o ' o « n 0 0 0 0 0 0 o o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 69 290 R e l a t i o n s h i p between pore p r e s s u r e and a x i a l s t r a i n i n an undrained . t e s t 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 70 3 0 „ T y p i c a l water c o n t e n t - s t r e s s r e l a t i o n s h i p s f o r s a t u r a t e d , n o r m a l l y c o n s o l i d a t e d remolded and i n s e n s i t i v e c l a y s o o o 71 3 1 0 R e l a t i o n s h i p between water content and s t r e s s a f t e r normal c o n s o l i d a t i o n and at ( o i " - 03 ') max0 and ( c i ' / o ^ ' ) maxo f a i l u r e •.criteria© 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 72 32o V a r i a t i o n of the m o b i l i z e d . e f f e c t i v e angle of shearing r e s i s t a n c e w i t h a x i a l ' s t r a i n 0 o o o o o o o o o o o o o o o o o o o o o o o o o o , 74 ACKNOWLEDGMENT This thesis is a contribution to the research program at the University of British Columbia on the strength and deforma-tion characteristics of cohesive s o i l s 0 The program, which is financed by the National Research Council of Canada under grants Noo 1498 and No„ 1507, i s directed by Dr 0 W0D0 Liam Finn, Professor and Head, Department of C i v i l Engineering,-and Professor N 0D„ Nathano The author i s grateful to Professor Nathan and Dr 0 Finn for their guidance and constructive criticism during the development and preparation of this thesis a The undrained test results were obtained by Mr0 Peter Byrne with whom the task of developing satisfactory testing procedures was shared„ Dr 0 EoHo Gardner, Department of Soil Science, kindly supplied data on the chemical properties of the clay. The technical assistance supplied by the staff:of the C i v i l Engineering Department Workshop i s gratefully acknowledged„ 1 CHAPTER 1 INTRODUCTION l o l Purpose Triaxial compression tests are a useful method of investigating the stress-strain behavior of s o i l , and in particular, of determining the shear strength of s o i l under drained and undrained conditions„ The stress-strain characteristics of cohesive soils have been the subject of exhaustive re-search in recent years 0 The need for a thorough understanding of these aspects of s o i l behavior i s increasing daily as the number of building sites ' containing acceptable cohesionless. foundation material rapidly diminishes, and the size of e a r t h - f i l l dams steadily increases 0 Two approaches have been used to study the response of s o i l to applied stresses and strains. The f i r s t approach, toward which most attention has been directed, examines the macroscopic behavior of s o i l in laboratory and f i e l d tests 0 This has led to the development of strength c r i t e r i a which satisfy the practicing engineer in his search for solutions to everyday problems, but has not re-vealed the fundamental properties governing soil., behavior 0 The second and more recent approach inquires into the nature of the physical and chemical bonds existing between individual s o i l particles and their environment, and has the ultimate goal of relating these properties to the macroscopic be-havior of the s o i l mass. Primarily as a result of the macroscopic approach to s o i l behavior, many empirical relationships have been proposed between s o i l strength and such variables as void ratio and effective stresso "Of particular interest to this investigation i s the concept of a common effective stress failure envelope determined from drained and undrained t r i a x i a l compression tests on saturated cohesive s o i l s 0 Many workers have confirmed the vali d i t y of 2 this concept for remolded clays (Hvorslev,1960)*0 In addition, attempts to explain the common envelope in terms of the fundamental'physico-chemical properties of remolded clays have met with limited success (Scott,1962) 0 Undisturbed clays, which possess characteristics significantly different from remolded clays, have not received as much attention as the latter, and published results of tests show conflicting data concerning the existence of a common envelope (Henkel,1960)0 It was the purpose of this.thesis to investigate, experimentally, the drained and undrained stress-strain behavior of a normally consolidated un-2 disturbed saturated clay of extra-sensitivity (Skempton and Northey,1952) , to report on the testing procedures used i n the investigation, and to examine the concept of a common failure envelope (independent of stress path) for sensitive clays 0 102 Scope The experimental phase of this project was conducted in conjunction with Mr0 PoMo Byrne, fellow graduate studento Consolidated drained and un-drained t r i a x i a l compression tests were performed at constant strain rate on undisturbed saturated samples of extra~sensitive elay 0 A l l samples were normally consolidated prior to shearingo The series of drained tests were performed by the author and the undrained tests, in which pore pressures were measured, were performed by Mr0 Byrne0 With the exception of the drain-age conditions and confining pressures, a l l features of both series of tests were identical„ A description of testing procedures i s contained in Chapter 2 0 Io A l i s t of references, arranged alphabetically, may be found at the end of this thesis 0 2 0 For a definition of sensitivity, the reader i s referred to section 402 of this thesiso 3 Many preliminary tests were performed before a satisfactory testing procedure was developed and a discussion of some of the problems encountered has been included in Chapter 3. The f i n a l test series consisted of six drained and six undrained tests (two at each of six confining pressures). A discussion of the shape of the stress-strain curves obtained i s included in Chapter 4, along with compari-sons of the drained and undrained strength envelopes determined for failure c r i t e r i a of maximum principal stress.difference (maximum deviator stress) and maximum effective principal stress ratio. The use of energy corrections to account for volume change i s discussed, and an estimate of the pore pressures developed in drained tests Is presented 0 The effect of rate of strain on the behavior of the clay i s briefly mentioned, A summary of the conclusions reached in this investigation i s presented in Chapter 5, and suggestions for further research may be found in Chapter 6. The nomenclature used throughout this thesis conforms to that adopted by the American Society of C i v i l Engineers (1962). A l l symbols are defined as they occur and for convenience, a table of nomenclature, assembled alphabetically, i s included at the end of this thesis. 4 CHAPTER 2 DESCRIPTION OF SOIL TESTED AND TESTING PROCEDURES 2ol D e s c r i p t i o n of s o i l The c l a y deposit from which the b l o c k samples were taken i s l o c a t e d at Haney, B r i t i s h Columbia, which i s about t h i r t y m i l e s east of Vancouver on the n o r t h bank of the F r a s e r R i v e r , The deposit i s the present s i t e of a b r i c k p l a n t which uses the c l a y i n the manufacture of b r i c k and t i l e 0 The s o i l i s known l o c a l l y as Haney c l a y and t h i s name w i l l be adopted i n t h i s thesis, , D e p o s i t i o n of the m a t e r i a l apparently occurred d u r i n g or s h o r t l y a f t e r the l a s t major g l a c i a t i o n of south-western B r i t i s h Columbia at a time when the sea was h i g h e r ( r e l a t i v e to the land) than i t i s at present (Armstrong, 1957)o Thus the d e p o s i t was formed i n a marine or b r a c k i s h environment„ Subsequent u p l i f t of the land has permitted l e a c h i n g of the s o i l to o c c u r , l e a v i n g i t with a s e n s i t i v e s t r u c t u r e . The c l a y p r e s e n t l y comprises a s u r -face deposit covered only by a t h i n l a y e r of Weather s o i l , , a n d i s only l i g h t -l y o v e r - c o n s o l i d a t e d i n s i t u . Haney c l a y c o n t a i n s approximately h o r i z o n t a l l a m i n a t i o n s of medium to f i n e s i l t and c l a y . The l a m i n a t i o n s are of v a r y i n g t h i c k n e s s e s . The c l a y i s a dark b l u e - g r e y c o l o r when wet, the c o l o r of neat cement when d r y , and has l i t t l e o r g a n i c odor. Evidence of i t s d e p o s i t i o n s ! environment i s o f f e r e d by the e x i s t e n c e of s m a l l marine s h e l l s which may be found i n the c l a y . Results of standard l a b o r a t o r y i d e n t i f i c a t i o n t e s t s performed on samples of Haney c l a y may be found i n Table I and F i g u r e s 1 and 2. 5 TABLE I PHYSICAL PROPERTIES OF HANEY CLAY s S p C C i l f l r C gravity o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o b o o o o o o o o o o 2 o 8 0 Liquid X i l C l i t o o o o o o o o o o o o o o o o o o o o o o o o o o o o b o o o o o o o o o o o o o o o o o o o o o 44/> Plastic l i l t t i t o O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O o o o o o o o o o o o o 2 6 ^ Plasticity illdeX o o o o o o o o o o o o o o o o b o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 18/o* Natural Water COntent o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o b o o ' a o o o o o o 42 /o 4" l> o Percent finer than 2 m i c r o n s 0 0 o o o o o 0 0 o o o o 0 o o o o o o o o o o o o o o o o o o o o 4 6 % A c t i v i t y o O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O o O o 3 9 Undisturbed unconfined compressive s t r e n g t h o 0 o o o o o o o o o ° o o o o o 1 0 o 8 l b s 0 / s q 0 i n 0 Remolded unconfined compressive s t r e n g t h o o 0 o o o o o 0 o o o o o o o o o o 0 0 0 0 9 lbs 0/sq 0 i n 0 Sensitivityo 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o l 2 Maximum past p r e s s u r e 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 8 lbso/sqo ino M. I. T. GRAIN SIZE CLASSIFICATION FINE SAND COARSE SILT MEDIUM SILT FINE SILT COARSE CLAY MED KlAYj O.IO 0.05 0.02 0.01 0.005 0.002 0.001 0.0005 GRAIN DIAMETER (MMS) FIGURE I. GRAIN SIZE DISTRIBUTION OF HANEY CLAY 7 FIGURE 2. T Y P I C A L STANDARD CONSOLIDATION C U R V E FOR H A N E Y C L A Y . 8 A small dry sample of the s o i l was subjected to x-ray diffraction analysis to determine the mineral composition of the clay. Results of this test may ' be found in Table II, The following testing procedures are the fi n a l procedures adopted0 Other procedures were tried and abandoned for various reasons, some of which are discussed in Chapter 3, 202 Sampling and storing A l l samples were obtained by hand excavation from the clay deposit at Haney (Figure 3)<> After removing a l l the disturbed surface material from a 12 square foot area, 9 i n 0 by 9 i n 0 by 9 i n 0 block samples were excavated using a fine wire saw0 The blocks were immediately coated with a layer of Mobile #2300 wax and transported to the laboratory. In the laboratory, the blocks were given further coatings of wax to ensure that there would be no change of water content during storage. The waxed blocks were stored in a moist room u n t i l used, 2,3 Preliminary tests As previously mentioned, standard identification tests were performed on the clay prior to conducting the main series of experiments. These tests included the determination of natural water content, specific gravity, Atterberg limits, grain size, unconfined compression strength, sensitivity, maximum past pressure and coefficient of consolidation (Table 1, Figures 1 and 2)o A l l of these tests were performed in accordance with the procedures suggested by Lambe (1958). TABLE II CHEMICAL PROPERTIES OF HANEY CLAY GRAIN SIZE . MINERAL AMOUNT PRESENT Quartz Large S i l t fraction Feldspar Large (greater than Chlorite Moderate - small 2 microns) Mica Moderate - small Amphibole Small Chlorite Large Clay fraction Feldspar Moderate = small (less than Mica/chlorite Moderate - small 2 microns) Quartz Small Mica Small Amphibole Small <= questionable Figure 3: Sampling the c l a y . 11 2,4 Preliminary Considerations The clay was brought to f a i l u r e by the application of a constant rate of a x i a l strain,, The choice of a suitable rate of deformation was based on the c r i t e r i a that minimal pore pressures should be present over most of a drained stress path, and that adequate pore pressure equalization should be present over most of an undrained stress path 0 Because the use of side drains generally hastens the dissipation or equalization of pore pressures, t r i a l t r i a x i a l consolidation tests were performed using Whatman8s No, 54 f i l t e r paper side drains (Bishop and Henkel,1962), Other t r i a x i a l consolidation tests were performed without the aid of side drains and although the use of f i l t e r papers did hasten the rate of consolidation, the increase was not significant,, In view of t h i s and because side drains are d i f f i c u l t to place around the sample, i t was decided not to use f i l t e r papers, but to permit drainage from the top and bottom of the sample only 0 Calculations based on the method of obtaining rates of deformation suggested by Bishop and Henkel (1962) indicated that, under the above drainage conditions, a rate of s t r a i n of 0,25 percent per hour was satisfactory i f f a i l u r e occurred at 15 percent a x i a l s t r a i n i n the drained tes t s . I t was subsequently determined that drained f a i l u r e would occur at approximately 30 percent a x i a l s t r a i n and thus a rate of s t r a i n of 0,50 percent per hour was believed adequate. The choice of satisfactory e f f e c t i v e confining pressures was governed by the following requirements; 1, A l l samples were to- be normally consolidated and therefore e f f e c t i v e confining pressures must ex-ceed the maximum past pressure (38 lbso/sq, in,) 2 0 The maximum allowable pressure i n the t r i a x i a l equipment i s 100 lbs,/sq, i n , , and 3, Because the test data obtained i n t h i s investigation was also to be used i n a separate study of drained and undrained e f f e c t i v e stress paths, the paths were to cross at convenient, well-spaced i n t e r v a l s . The effective confining pressures for the drained tests were 40 l b s , / s q 0 i n 0 , 55 lbs,/sq,in,, and 70 lbs,/sq,in, and for the undrained tests 60 lbs,/sq, i n , , 75 lbs,/sq,in,, and 88,5 lbs,/sq,in 0 2.5 Description and preparation of equipment A Clockhouse Engineering T010 t r i a x i a l c e l l capable of receiving 208 in, by 1„4 i n , diameter samples was used for a l l tests 0 Although drainage was permitted from both the top and the bottom of the sample, pore pressures were measured at the base of the sample only, using a Bishop and Henkel null indicator. Volume changes were measured i n a 10 cubic centimeter capacity burette, graduated to 0 01 cubic centimeters. To ensure complete saturation of the sample, a back-pressure of 10 Ibso/sqoin, was applied to the drainage line by means of a mercury column and balancing tank. A l l drainage leads and pore pressure lines were constructed of small diameter copper tubing except for the connection to the drainage burette which was of saran tubing. Valves used in the system were Hoke non-displacement valves (incorporating teflon seals) and Hoke stem valves. Schematic diagrams of the equipment are shown in Figures 4 and 5, and a photograph of the equipment, taken during a preliminary undrained test, i s shown in Figure 6, Axial loads were measured by a proving ring and both the chamber pressure and pore pressures were measured by bourdon gauges0 The proving ring was calibrated against a Baldwin-Hamilton Universal Testing Machine and both bourdon gauges were calibrated against a dead weight tester prior to use. De-airing was accomplished by passing large quantities of warm, de-aired, d i s t i l l e d water through a l l the lines. The lines were then subjected to positive and negative pressures in excess of those anticipated during any test, A f u l l y reversible rise in the level of the mercury in the null tube DIAL GAUGE MACHINED SLEEVE A TO PROVING * RING LOADING CAP SAMPLE SATURATION SPIRAL MEMBRANES O l ® TO PORE PRESSURE r AND DRAINAGE SYSTEM VALVES X HOKE STEM (DISPL.) (J) KLINGER ABIO (NON-DISPL.) ( £ ) HOKE BALL (NON-DISPL.) POROUS STONE TRIAXIAL CELL CLOCKHOUSE TYPE T.IO POROUS STONE 0-RINGS REGULATORS / \ STRAIN CONTROLLED AX.AL DRIVE j W H £ £ V | IN. O.D. IMPERIAL POLYETHYLENE TUBING I— DE-AIRED WATER IN. O.D. COPPER PRESSURE SUPPLY _ VACUUM I SUPPLY CONTROL PANEL STEEL BALANCING TANK CHAMBER PRESSURE GAUGE (0-100 LBS./SQ.IN.) NOT TO SCALE FIGURE 4. TRIAXIAL CELL AND CHAMBER PRESSURE SYSTEM DISTILLED DE-AIRED WATER SUPPLY CONNECTIONS TO TRIAXIAL CELL-' (7) LOWER STONE (?) UPPER STONE •0 8 IN. O.D. COPPER 3 IN.O.D. COPPER BISHOP AND HENKEL NULL INDICATOR PRESSURE CONTROL CYLINDER 10 CU. CMS. BURETTE (ADJUSTABLE HEIGHT) -7 IN. O.D. IMPERIAL 4 POLYETHYLENE TUBING VALVES X HOKE STEM (DISPL.) KLINGER ABIO (NON-DISPL.) (S) HOKE BALL (NON-DISPL.) JL 0 PORE PRESSURE GAUGE (0-100 LBS /SQ. IN.) ^ - | N . o.D. SARAN 1 6 TUBING BALANCI TANK NG 4 4 FT. MERCURY MANOMETER TO MEASURE NEGATIVE PORE PRESSURE \ OVERFLOW 4 FT. MERCURY " MANOMETER TO SUPPLY 10 LBS /SQ. IN. BACK PRESSURE NOT TO SCALE FIGURE 5 DRAINAGE AND PORE PRESSURE MEASURING SYSTEM Figure 6 : Triaxial equipment. 16 of about 1/2 inch per 100 lbs,./.sq.in,, was achieved thus indicating the pore-pressure equipment was satisfactorily de-aired, No change in level of the water in the drainage burette was observed when the pressure in the drainage lines was increased to 25 lbs,/sq.in. No measurable evaporation occurred in the drainage burette 0 206 Test preparation sample trimming and placing Before commencing each test, a l l drainage lines were flushed with de-aired d i s t i l l e d water0 Two porous stones were placed in boiling water for half-an-hour to ensure complete saturation. The stones were then allow-ed to coolo The circumferences of the base pedestal and the loading cap were coated with silicone grease before placing a rolled membrane (Sheik natural rubber, 0,003 in, wall thickness) around each of them. Four rubber 0-rings were slipped onto ring expanders and placed around the saturation spiral in preparation for binding the membranes to the pedestal and the loading cap. The samples were prepared in a humid atmosphere to reduce sample mois-ture losses, and were trimmed with a fine wire saw to approximately 1.4 in, diameter by 2,8 in, length, using a procedure similar to that recommended by Bishop and Henkel (1962), The prepared sample and trimming tools are shown in Figure 7, Four large (approximately 40 gm, wet weight) side samples were removed from evenly spaced locations around the sample and the water content of each was determined. These were averaged to obtain the i n i t i a l average water content of the sample. Water content determinations of the end trimm-ings were also made but not used because the laminated nature of the s o i l rendered then unrepresentative. Due to the sensitive nature of the material, extreme care was taken to keep handling of the sample to a minimum. The whole sample was weighed prior to placing i t in the t r i a x i a l c e l l . Figure 8: Sample i n p l a c e on t r i a x i a l base. .The procedure adopted for placing the sample i n the c e l l was as follows; A previously soaked porous stone was ca r e f u l l y s l i d into a convex water meniscus covering the base pedestal, and the sample was car e f u l l y placed on the stone. The top porous stone was then s l i d onto a convex water meniscus covering the inverted loading cap and the whole upper assembly (cap and stone) was righted and s l i d onto the top of the sample 0 A small: quantity of water was permitted to flood both porous stones and the lower membrane was then r o l l e d up around the sample. This membrane was coated with s i l i c o n e grease and the second membrane r o l l e d down over the f i r s t . Two 0=>rings were placed around both the top loading cap and base pedestal. Figure 8 shows the sample, stones, loading cap, membranes, and 2 of the 4 0-rings i n place ? The v e r t i c a l alignment of the sample, stones, and load-ing cap was checked o p t i c a l l y with an engineer's t r a n s i t . The chamber was then placed on the t r i a x i a l base and the loading ram was brought into con-tact with the loading cap and aligned with the sample and the base of the proving ri n g . Again, the t r a n s i t aided i n t h i s alignment, 2 , 7 Application of chamber pressure, sample saturation and i n i t i a l  consolidation De-aired water was permitted to enter the t r i a x i a l chamber under 15 lbs,/sq.in, gauge pressure during which time no drainage was allowed to or from the sample. The sample was checked for complete saturation by r a i s i n g the chamber pressure to the desired value i n increments of 10 lbs,/sq,in. The change i n pore pressure corresponding to each of these increments was recorded and thus values of the pore pressure parameter B (Skempton, 1954) were determined. The increments of pressure were applied at four minute intervals and B values of l o 0 (indicating complete saturation) were obtained. After the desired chamber pressure was applied, the sample was allowed to consolidate for exactly 24 hours at which time a l l excess pore pressures had e f f e c t i v e l y d i s s i p a t e d (time f o r 90 percent c o n s o l i d a t i o n to occur, tgg, never exceeded 200 minutes). During c o n s o l i d a t i o n , care was taken to maintain v e r t i c a l alignment by ensuring the bottom of the l o a d i n g ram r e -mained i n contact w i t h the l o a d i n g cap as the sample decreased i n volume. This was accomplished by r a i s i n g the l o a d i n g p l a t f o r m u n t i l a s m a l l d e f l e c -t i o n r e g i s t e r e d on the proving r i n g d i a l gauge i n d i c a t i n g that the ram was bearing on the l o a d i n g cap, 2.8 Drained shear t e s t s Upon completion of the 24 hour c o n s o l i d a t i o n p e r i o d , the sample was sheared by a p p l i c a t i o n of a constant a x i a l s t r a i n r a t e of 0,014 i n s , per hours (0,5 percent per hour). Shearing was continued u n t i l s h o r t l y a f t e r the peak s t r e n g t h was reached which u s u a l l y occurred at about 30 percent s t r a i n . Thus the shearing process, was continued f o r about 65 hours, A photograph taken during a p r e l i m i n a r y shear t e s t i s shown i n Figure 9, Elapsed time, volume change, a x i a l l o a d , a x i a l deformation and temperature were recorded throughout the t e s t and a complete:set o f . t y p i c a l t e s t data ( f o r t e s t S-17) may be found i n the Appendix, 2.9 Undrained shear t e s t s In the undrained shear t e s t s , pore pressures were measured w i t h a Bishop and Henkel n u l l i n d i c a t o r . Minor m o d i f i c a t i o n s were made to the t e s t i n g equipment a f t e r the drained t e s t s e r i e s was completed to ensure a more s a t i s f a c t o r y supply of d e - a i r e d chamber water. The i n s t a l l a t i o n of an a i r c o n d i t i o n e r permitted b e t t e r temperature c o n t r o l d u r i ng the undrained t e s t s than was maintained during the drained t e s t s . Complete inform a t i o n on the undrained t e s t r e s u l t s ( i n c l u d i n g t y p i c a l t e s t data) may be found i n Byrne (1966), Figure 9: Sample during shear. 21 2.10 Back-drainageo dismantling, and cleaning Before removing the.sample from the chamber, the chamber pressure was lowered to approximately 2 l b s o / s q . i n , , above the back pressure, and the loading ram was raised off the loading capo Water was then permitted to drain back into the sample from the drainage burette u n t i l any negative pore pressures had dissipated (Henkel and Sowa, 1963) 0 The quantity of water entering the sample was measured so that the change i n water content deter-mined from i n i t i a l and f i n a l weights could be checked against volume chan-ges measured i n the burette. After back-draining was complete, the chamber was dismantled and the sample removed, weighed and measured0 The sample was then dried to determine i t s f i n a l water content 0 After each te s t , a l l drainage l i n e s were again flushed with de-aired, d i s t i l l e d water,, The loading cap and base pedestal were thoroughly washed i n commercial detergent to remove a l l d i r t and grease thus reducing the p o s s i b i l i t y of trapping a i r i n the equipment i n the following t e s t 0 CHAPTER 3 DISCUSSION OF TESTING PROCEDURES 3 d Introduction As the experimental work proceeded, i t became obvious that there was no such thing as a routine test, and much time was spent before satisfactory test procedures were determined, A discussion of some of the test proce-dures f i n a l l y adopted i s included in this chapter. Certain procedures which were found undesirable are discussed, and further improvements are suggested, 3.2 Sampling, waxing and storing Field sampling took place on a very warm day. The surface of the Haney clay dried v i s i b l y during sampling and therefore exposed layers of clay were removed just prior to waxing. Subsequent tests (Section 2,7).indicated that the sampled clay was effectively 100 percent saturated and thus the above precaution was believed adequate. The blocks were covered with a 1/4 inch to 1/2 inch wax layer for stor-age. As the samples were stored for a longer period of time than originally anticipated (9 months instead of 3 months), i t is f e l t that a thicker layer of wax would have been desirable. Periodically the blocks were checked for signs of moisture loss or gain. The extent to which water had leaked into the blocks was measured by the color change that the clay underwent during this process. Two of the blocks were rewaxed when i t was discovered that a small quantity of water had leaked into them0 Prior to rewaxing, the clay which was contaminated was trimmed from the blocks and discarded, 3.3 Sample preparation The sample was trimmed on a perspex lathe and miter box (Figure 7), Although the resulting sample was adequate, small imperfections in the per-spex (such as warping) made i t very d i f f i c u l t to obtain a sample with parallel ends exactly at right angles to i t s sides•<,. This resulted in alignment d i f f i c u l t i e s when placing the sample in the t r i a x i a l c e l l , A brass trimming lathe and miter box: would probably eliminate this problem. Due to the highly variable nature of the clay in the vertical direc-tion, every care was taken to ensure that each t r i a x i a l sample came from the same vertical elevation. Because the laminations were not of regular thickness and only approximately horizontal (insitu), i t was necessary to trim the sample so that the laminations became horizontal when placed in the t r i a x i a l c e l l . Thus i t was hoped to avoid the possibility of the sam-ple undergoing irregular consolidation and therefore buckling prematurely when sheared. In spite of these precautions, three preliminary samples did buckle but i t i s not known whether buckling was due to the irregular nature of the material or faulty alignment of the equipment. The horizontal varia-tion of water content within the clay made i t necessary to attempt to con-duct the f i n a l series of tests on samples taken from a single block. How-ever, only five or six samples could be trimmed from each block and therefore more than one block was used. Fortunately, no significant variation between the blocks used was observed, 3,4 Water content and volume measurements As mentioned i n Section 3,3, the water content of the clay varied both vertically and horizontally. Variations i n water content of up to 8 percent in 3 vertical inches and of up to 2 percent in 3 horizontal inches were measured. It was feared that, because of this variation, the side trimmings would not yield representative average water contents. Therefore four tests were performed in which the average water content of four side trimmings was compared with the water content of the whole sample. These specimens were prepared in exactly.the same way as those used in the fi n a l test ser-ies but were neither consolidated nor sheared. Although the individual side trimmings showed up to 1,0 percent deviation from their average, the average i t s e l f did not deviate more than 0,2 percent from the.measured water content of the. whole sample (see Table III), It was therefore concluded that the side sample method of obtaining the i n i t i a l water content of the specimen was satisfactory. Trimmings taken from the top and bottom of the specimen were not representative of the whole sample because they contained a pre-dominance of one lamination. The i n i t i a l volume of the specimen was determined by measuring i t s length in four places and i t s circumference at the top, middle, and bottom. These measurements invariably resulted i n the calculated i n i t i a l saturation value exceeding 100 percent. Because tests on various samples of Haney clay had indicated that the specific gravity of the s o i l was constant (»2,80) although the clay was highly laminated (Section 2 03), and because the water content of the sample was believed to be accurately known (see above para-graph) , i t was assumed that the error in the calculated degree of saturation stemmed from an error in measuring the volume. Therefore a new volume was calculated assuming 100 percent saturation. Since circumference measurements were the most d i f f i c u l t to make, i t was assumed that a measuring error occur-red there, and thus the cross-sectional area of the sample was corrected to conform to the calculated volume. The measured i n i t i a l length was assumed correct, and the corrections to the area were always small (the calculated volume never differed from the measured volume by more than 1 percent), 3,5 Test equipment Compressed air from a house line was delivered to the equipment at 128 lbs,/sq, i n . I n i t i a l l y , the air was passed through one regulator to supply the desired chamber pressure. However, regulation was poor and a 25 T A B L E I I I / / W A T E R C O N T E N T S O F S I D E T R I M M I N G S C O M P A R E D T O T H E WATER C O N T E N T O F T H E WHOLE S A M P L E W A T E R C O N T E N T (%) T E S T T R I M M I N G S WHOLE N O , S I D E S A V E R A G E S A M P L E 1 3 7 o 5 3 7 0 1 3 7 0 4 3 7 0 5 3 7 0 4 3 7 0 4 2 3 7 0 6 3 6 0 4 3 6 0 3 3 8 0 1 3 7 0 1 3 7 „ 2 3 3 7 o 9 3 7 o O 3 7 o 0 3 6 0 8 3 7 c 2 3 7 c 3 4 3 7 o 2 3 6 0 7 3 7 0 2 3 6 0 6 3 6 0 9 3 7 0 1 second regulator was Installed in series with the f i r s t 0 No further regula-tion problems were encountered,, The back pressure of 10 lb8 0/sq,in, was supplied by a column of mercury connected to a 1200 cubic inch capacity balancing tank* The tank was required to prevent pressure fluctuation dur-ing drainageo A l l measured pressures were corrected to a standard elevation (the center of the sample). Chamber pressures and pore pressures were measured by 0=100 lbs 0/sqoin 0 bourdon gauges which were calibrated against a dead weight tester prior to use 0 It was observed that the bourdon tubes crept irregularly under pressure and from time to time, further calibration was necessary. It is suggested that el e c t r i c a l pressure transducers may prove more reliable for these measurements. The t r i a x i a l c e l l contained a machined stainless steel loading ram which was lubricated at the start of each test. By measuring the force required to move the ram at a constant rate against a chamber pressure, i t was observed that the f r i c t i o n did not vary as different sections of the ram came in contact with the collar. Prior to each shear test, the ram was run for about an hour at the test deformation rate and against-the test chamber pressure to determine the "zero" proving ring reading, A double ring proving ring was used to measure axial loads and i t was calibrated against a Baldwin-Hamilton Universal Testing Machine, The only problem encountered with the proving ring occurred when the inner ring began to deflect. The point at which this took place was not well defined and had to be calculated for each test by plotting ring deflection against time. The deflection at which an abrupt change in slope occurred represented the reading at which the new calibration curve became applicable. The use of a strain.gauge embedded in the loading ram appears to'be a promising alterna-tive method of measuring axial loads. If the strain gauge is placed inside 27 the t r i a x i a l c e l l , the loads measured are true sample loads and are not affected by ram f r i c t i o n at the c e l l head. I n i t i a l l y , glycerin was used as a chamber f l u i d (Lame,1958)0 However, leakage out of the sample was observed at a l l chamber pressures. It waB subsequently discovered that previous investigators (Poulos, 196A) had re-ported this problem and recommended that de-aired water be used as the cham-ber fluido With de-aired water in the chamber, no further leakage though the membranes or bindings was observed, Pressure was:applied to the chamber water at an air-water interface located in a balancing tank at the end of a four foot length of 3/8 in„ outside diameter polyethylene tubing leading from the chamber0 This arrangement prevented dissolved air permeating the water in the t r i a x i a l chamber (Poulos, 1964), The drainage system included six valves 0 Originally three Klinger AB10 non-displacement valves were installed but were found to leak e r r a t i -cally. They were replaced by three stainless steel Hoke non-displacement valves which incorporate teflon seals, and no further problems were encount-ered. The other three valves were brass Hoke stem valves which performed very satisfactorily. An admittedly undesirable air-water interface was per-mitted in the drainage burette. However, no evaporation losses were measur-ed during a one week test period and although the meniscus was occasionally misshapen, i t rarely presented any reading d i f f i c u l t i e s . It has been mentioned that the use of f i l t e r paper side drains was abandoned because they offered few advantages (Section 2,4). The reason that they did not substantially increase the rate of drainage is believed to stem from the extra-sensitive nature of the clay. It is thought that trimm-ing disturbed (smeared) the structure of the clay at the edge of the sample, thus creating an effectively impermeable barrier to drainage to the sides. The sample was protected by two membranes with a layer of silicone grease between them0 I n i t i a l l y only one membrane was used but i t was found to be too permeableo Both the loading cap and- base pedestal were greased around their circumferences to reduce leakage past the 0-rings, Two rubber 0-rings were placed around the loading cap and two were placed around the base pedestalo The unstressed dimensions of the 0-rings were 1,46 ins 0 out-side diameter by 0,125 ins 0 thick 0 The O-rings were moved into position on 1,6 ins, outside diameter brass ring stretchers, and in placing the 0-rings, care was taken to avoid "s p i r a l l i n g " (Poulos, 1964), Leakage through the membranes and past the bindings i s believed to be reduced to a tolerable level in tests lasting up to 100 hours i f the above procedures are adopted,, It i s suggested by Bishop and Henkel (1962) that a correction should be applied to the measured principal stress difference to allow for membrane restrainto Based on their assumptions that the sample deforms as a right cylinder, with the sample and membrane acting as a unit, the correction was found to be 0,5 lbs,/sq,in, at 30 percent axial strain. It was observed that the membrane buckled during the drained tests and therefore-developed hoop tension. Calculations (Henkel and Gilbert, 1952) indicated that the hoop tension correction (to be applied to the radial stress) was about 0,3 lbs,/ sq,in. at 30 percent axial strain,, Because of the small magnitude of these corrections, and because of the limited validity of the assumptions on which the calculations were based, i t was decided to ignore the membrane correc-tions. Alignment of the sample, stones and loading cap was accomplished with the aid of a transit. Alignment was maintained during the consolidation phase by ensuring that the loading ram remained in contact with the loading cap. If good alignment was not achieved, the samples buckled, particularly 29 since the loading cap was completely free to rotate and did not resist buckling, A sample was considered to be buckled i f the loading cap rotated through 2 degrees. Usually i t was observed that i f rotation exceeded 2 degrees (as i t did i n three preliminary tests), the system became unstable and rotation continued un t i l the test was stopped. Although a fixed load-ing head is recommended for undisturbed so i l s (Bishop and Henkel, 1962), i t is believed that a free head i s superior because i t does not induce unmeas-ured stresses in the sample when the tendency to buckle is present. It was observed that i f care is taken when aligning the equipment, freely rotating loading heads can be successfully used on highly laminated undisturbed s o i l s . The air temperature in the laboratory was manually controlled to be-tween 23°C and 26°C during the drained tests. The installation of an air conditioner permitted air temperature control of 24°C + 0,2°C during the undrained tests. The temperature of the sample did not vary to the same extent as that of the air due to the insulating effect of the surrounding chamber f l u i d . However, a l l ancillary equipment was not so insulated and was thus subjected to similar temperature variations to the surrounding, a i r . Although the strain controlled t r i a x i a l machine delivered a constant rate of deformation to the t r i a x i a l c e l l , the deflection of the proving ring imparted a rate of strain to the sample which gradually increased during a test. Since this occurred in a l l tests, i t can be removed as a variable when comparing results within this investigation. The porous stones used in these experiments did not permit any lateral movement of the ends of the sample. This was evidenced by the bulbous shape of a l l failed samples. The end restraint, which creates a "dead zone" in either end of the sample, is a possible source of error in the t r i a x i a l test since i t introduces stresses which cannot be measured. At low strains, 30 these stresses may not be great, but at the large strains developed in this series of tests, they may indeed have been significant, The stresses have been computed on the basis of a corrected cross-sectional area calculated on the assumption that the sample deformed as a right, cylinder. At 34 percent axial strain, the cross-sectional area of the center of the sample was about 40 percent greater than that at the ends, and thus the physical significance of the stresses calculated at high strains is questionable. However they are s t i l l valid for comparison purposes. CHAPTER 4 DISCUSSION OF TEST RESULTS 4 o l Introduction Experimental data obtained during drained t r i a x i a l shear tests were recorded as shown in the Appendix which contains data from test S-17, Ex-perimental data obtained during undrained t r i a x i a l shear tests may be found in Byrne (1966), Both drained and undrained test data were analyzed on the University of British Columbia IBM 7 0 4 0 computer and a summary of some of the results of this analysis may be found in Table IV, [The data presented in Table IV has not been corrected for residual pore pressures developed during drained tests nor have the stresses been corrected for an "energy balance"]. These corrections w i l l be considered separately (Sections 4 , 3 and 4 , 4 ) , Wherever possible, two tests were performed at each confining pressure. This procedure offered a check on the r e l i a b i l i t y of the test data and also indicated the magnitude of the natural v a r i a b i l i t y of the clay. Less than two percent variation in measured properties was obtained for specimens taken from the same block samples as long as the precautions mentioned in Section 3 , 3 were observed. However, as reported in Section 3 , 3 , specimens taken from different block samples often exhibited larger variations than that just quoted, particularly in. i n i t i a l water.content. Although the re-sults reported herein were obtained from specimens taken from block samples having very similar properties, i t should be emphasized that the natural variability of the clay must be considered when comparing test results. The results are discussed under the headings: residual pore pressures developed during drained shear tests, energy corrections, stress-strain re-lationships, and shear strength. The drained and undrained shear strength 32 TABLE IV SUMMARY OF TEST RESULTS Test No, c l b s , / 8 f l o l n t maxo .u>% e% max. w l e% Undrained shear late, of Jih&aJL • 0^5% oc J: hour C—U—l 60,0 36,1 2,4 35,4 2,43 24,6 36,1 17,6 25,7 3,04 30,3 C-U-2 60,0 36,3 2,1 34,5 2,27 22,8 36,3 17,1 25,4 3,08 30,6 C-U-3 75,0 34,1 2,6 40,6 2,35 23,8 buckli id C-U-4 88,5 33,5 4,1 45,9 2,50 25,4 33,5 18,6 38,3 3,06 30,5 C-U-5 75,0 33 0 y 3,6 39,4 2,46 24,9 33,7 15,0 33,0 3,06 30,5 C-U-7 88,5 33,1 4,0 47,2 2,54 25,8 33,1 14,8 41,7 3,07 30,5 AVGE, 3,1 2,42 24,5 16,6 3,06 30,5 s-12 S-13 S-14 S-15 S-16 S-17 AVGEt 40,0 55,0 70,0 70,0 '55,0 40o0 27,9 26,9 26,0 25,8 26,9 28,2 30,5 29,2 28,7 29,0 30,6 31,5 30,0 70,6 98,3 123,0 125,8 98,8 72,0 2,76 2,79 2,76 2,80 2,80 2,80 2,78 28,0 28,1 28,0 28,2 28,2 28,2 tat*, nf ahttflr - O.S2 par hmir 28,1 Drained shear Rate of shear » 2,5% S-10 40,0 j 26,6 I 31,9j70,6 |2,76 ^8,0 SSL hour 33 i s considered both from the maximum p r i n c i p a l stress difference f a i l u r e c r i t e r i o n and the maximum ef f e c t i v e p r i n c i p a l stress r a t i o f a i l u r e c r i t e r i o n . Before discussing these topics, a few comments on s e n s i t i v i t y and structures are presented, 4,2 S e n s i t i v i t y and Structure The s e n s i t i v i t y of clays has been defined i n numerous ways (Lambe, 1958), The most common d e f i n i t i o n which was o r i g i n a l l y proposed by Terzaghi (1944), and which has been adopted i n t h i s thesis i s 2 S e n s i t i v i t y • S • undisturbed peak strength , o o o o , o o o , , ( l ) remolded peak strength Skempton and Northey (1952) and Rosenqvist (1952) indicated that s e n s i t i v i t y i s primarily a result of leaching (reduction of the s a l t concentration i n the pore f l u i d ) , although thixotropy i s believed to be responsible for some low to medium s e n s i t i v i t y , Haney clay, which has a s e n s i t i v i t y of 12, i s classed as an extra-sensitive clay (Skempton and Northey, 1952), Investigations into the microcharacteristics of clays have shown that the structure which a clay develops during deposition i s : largely dependent on the concentration of e l e c t r o l y t e i n the pore f l u i d (Lame, 1958a), I f the pore f l u i d i s s a l i n e , a cardhouse (flocculated or edge-to-face) struc-ture i s l i k e l y to develop which becomes unstable under applied shear stress-es i f the s a l i n i t y of the pore f l u i d decreases. This change i n structure leaves the s o i l with reduced strength thus giving r i s e to the phenomenon of s e n s i t i v i t y . The exact manner i n which the chemical properties of the clay minerals and the surrounding pore f l u i d affect the structure of the clay i s not known, and although some st r u c t u r a l phenomena are understood, l i t t l e quan-t i t a t i v e knowledge of the influence that structure has on the s t r e s s - s t r a i n behavior of a clay i s available 0 It i s known, however9 that the remolding of the clay structure which occurs during shear, tends to create a more parallel (dispersed) arrangement of the platey-like clay particles, This rearrangement of the structure, along with any changes in void ratio which may occur, affects the magnitude of the forces existing between the individ-ual particles which in turn i s reflected in the stress-strain behavior of the clay, Scott (1962) has suggested that a clay with an i n i t i a l l y floccu-lated structure, regardless of whether subjected to drained or undrained shear, exhibits ah unstable stress-strain curve with a more or less marked peak. The peak represents the maximum shearing stress required to break the interparticle contacts and to slide particles over each other, When the contacts have been disrupted, failure continues at a lower level of shearing stress compatible.with the: more dispersed structure now present. On the other hand, a clay with an. i n i t i a l l y dispersed structure exhibits a resistance to shear which gradually increases with deformation u n t i l a constant shearing resistance i s reached. This type of curve i s stable and is usually not as s t i f f as.the stress-strain curve exhibited by a floccu-lated clay. Detailed discussions of the; physico-chemical properties of clays and of the role of structure in stress-strain behavior may be found in Grim (1953), Lambe (1958a, 1958b), Seed, Mitchell and Chan (I960), Leonards (1962), and Scott (1962), 4y.3 Residual pore pressure developed during drained shear tests The principle of effective stress developed by Terzaghi (1923) states that the strength and deformation characteristics of any s o i l are a function of the effective stresses acting in that so i l , , The effective stress (o'), acting on a plane, i s defined as the total stress (o) acting on the plane minus the pore pressure (u) 0 35 That i s ; (2) Thus, in a laboratory test, i f any meanful relationship i s to be proposed between strength and applied stress, or deformation and applied stress, the magnitude of the pore pressure developed during the test must be known0 Using the method suggested by Bishop and Henkel (1962), i t is possible to compute a deformation rate for drained tests such that the pore pressures developed during shearing are effectively (theoretically 95 percent) d i s s i -pated prior to any desired axial strain,, If the strength of the s o i l being tested i s the only information required, then the governing deformation usually chosen i s the failure strain. If a complete stress path is wanted, as was the case in this investigation (see Byrne, 1966), the strain at which most of the pore pressure must be dissipated i s determined by the f i r s t significant reading that i s required. Even at very slow rates of strain, measurable pore pressures are believed to exist in the early stages of a drained test and, although this fact i s widely recognized, few researchers have attempted to estimate the magnitude of the developed pore pressures and the affect that they may have on the subsequent behavior of the s o i l 0 By assuming that the load i s applied in discrete increments during a strain controlled test, i t i s possible to estimate the pore pressures pre-sent at any time using the one-dimensional consolidation theory developed by Terzaghi (1925), In this theory, the relationship between excess pore pressure and time i s given by the equations 2 c 6 u 6u 6t o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o (3) where c m coefficient of consolidation • v k » permeability e * void ratio a v " coefficient of compressibility Y u • unit of weight of water g • distance from the surface of the clay layer u «• pore pressure at time t Solution of Equation (3) for the case of drainage from both ends of a t r i a x i a l sample yields the approximate non-dimensionalized expressions; » tr 2 m ^ U p (U ^ 60/£) ooooooooooooooooooooaoooooo (4) T y » -0o9332 l o g 1 Q (1-U) -0o08519 (U » 60%) , H . . , „ . „ . . ( 5 ) where T - time factor v d • one-half the length of the sample U « average degree of consolidation ™ 1 - ~ u^ » i n i t i a l excess pore pressure Thus the theory requires knowledge of the i n i t i a l excess pore pressure and the coefficient of consolidation applicable to each1 load incrementu Skempton (1954) has derived the following relationship between applied stress and pore pressure i n the t r i a x i a l tests Au » B (A03 +._A_ (Acj - AC3)) 0 0 0 0 0 0 0 0 0 0 0 0 0 ( 6 ) where Au » change in pore pressure A03»change in the total minor principal stress ha 1 •* change in the total major principal stress B «••pore pressure coefficient reflecting the degree of saturation present in the sample A » pore pressure coefficient reflecting the dilatancy of the sample 37 In the present investigation, the clay was saturated and therefore B - 100 (see Appendix)o Also the chamber pressure (03) was held constant and thus Equation (6) simplifies to 3 All n A AO j 0 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ( 7 ) It has been assumed that the value of A during drained tests, although not necessarily constant, i s not less than 1/3 nor greater than 1, It should perhaps be noted that in a sensitive material, the upper limit A-l i s open to question since A i s known to exceed 1 i n undrained tests 0 It i s a relatively simple task to determine the value of c v during con-solidation (prior to shearing), and also after failure either during unload-ing or further consolidation of the sample, but none of these determinations yield a value of c^ that i s directly applicable during the actual shearing process. Figure 10 contains values of c^ (calculated b y the square root of time f i t t i n g method developed by Taylor (1948)) plotted against mean effective stress (p 5 • "" *j 11 ^  ) for the oedometer, and for t r i a x i a l consolidation before shearing and t r i a x i a l unloading after shearing. One value of c^ determined from t r i a x i a l consolidation of a sample which had been subjected to undrained shear, i s also shown. Guided by these values, upper and lower bounds for c^ were chosen and are indicated by the boundaries of the cross-hatched area on Figure 10, For simplification of the computations i t was assumed that, over the stress range of the tests (40 lbs,/sq, in, < mean effective stress, p°, < 115 I b S o/sq, in), c v varied linearly with the logarithm of mean effective stress. The upper bound was chosen to coincide both with the value of c^ obtained from t r i a x i a l consolidation at p 1 » 40 lbs,/sq, in, and with the value of c y obtained from oedometer tests at p 5 • 115 lbs,/sq, i n . The lower bound was drawn parallel to the upper bound such that, over the stress range investi-gated, the lower bound was never less than the smallest value of c^ determined from t r i a x i a l unloading after drained shear. ALL VALUES PLOTTED AT MEAN OF LOAD INCREMENT C v OBTAINED DURING FURTHER CONSOLIDATION AFTER UNDRAINED SHEAR PROBABLE RANGE OF C v DURING SHEAR TRIAXIAL UNLOADING AFTER DRAINED SHEAR 10 20 30 40 50 60 70 80 90 100 MEAN EFFECTIVE STRESS (LBS. / SQ. IN.) FIGURE 10. RELATIONSHIP BETWEEN COEFFICIENT OF CONSOLIDATION AND MEAN EFFECTIVE STRESS 39 From Figure 10, the upper bound of iss 2 c y m f l X - ( 0 „ 0 2 0 0 - O o 0 0 7 5 log 1 0p°> ins, / m i n 0 o 0 o , o 0 o o o 0 o o o o o o o o 0 ( 8 ) and the lower bound iss 2 C v min, " ^ O o 0 1 6 7 " 0 » Q 0 7 5 l o8io p 9^ i n S o / f f l i f t ' » « » « » » « » » « » « » » o o . c ( 9 ) With an estimate of the upper and lower bounds of A and c^ obtained above, the pore pressures present at any time during a drained test can be estimatedo Figure 11 shows the values of pore pressures calculated from a typical drained test (test S - 1 7 ) , for various combinations of the bounding values of A and c^o It can be seen that the lower bound pore pressures (calculated using the upper bound value of r and A • 1 / 3 ) represent less than 10 percent of the effective confining pressure, but that the upper bound pore pressures (calculated using the lower bound value of and A « 1 ) are in excess of 30 percent of the effective confining pressure. In the latter case, although these pore pressures are mainly dissipated within 5 percent axial strain, they do not completely dissipate u n t i l failure occurs at 30 percent axial strain. Figure 12 i s a graph of effective principal stress ratio versus axial strain for test S - 1 7 and shows what effect the above pore pressures have on the effective principal stress ratio. For the lower bound pore pressures, the increase in effective principal stress ratio over that obtained assuming no pore pressures, is only slight, and is not noticeable beyond 3 percent axial strain. In the case of the upper bound pore pressures, not* only is the effective principal stress ratio increased at a l l strains except close to failure, but also the shape of the effective principal stress ratio - axial strain curve i s substantially changed, exhibiting a small peak at 1 , 5 percent axial strain. Thus the development of pore 14 AXIAL STRAIN (%) FIGURE II. RELATIONSHIP BETWEEN COMPUTED PORE PRESSURE AND AXIAL STRAIN IN A DRAINED TEST. 41 FIGURE 12. SHOWING THE EFFECT OF COMPUTED PORE PRESSURE ON THE EFFECTIVE PRINCIPAL STRESS RATIO IN A DRAINED TEST. 42 pressures can lead to quite different values of effective principal stress ratio than those obtained assuming no pore pressures„ What effect these adjustments have on s o i l behavior i s not known, but there is no reason to assume that the subsequent deformation characteristics of the s o i l do not reflect any changes in effective principal stress ratio that may occur 0 No further use of these computed pore pressures has been made in this thesis because of the uncertain nature of the assumptions upon which the calculations are based 0 However, i t i s believed that before f u l l y meaning-fu l comparisons of "drained" and "undrained" tests can be attempted, some allowance for residual pore pressures developed in drained tests must be made <, 4 o 4 Energy corrections Before discussing the application of energy corrections to the present data, a brief review of some of the publications dealing with this topic i s presentedo Following this, energy corrections proposed by Bishop ( 1 9 5 4 ) , Rowe ( 1 9 6 2 ) , and Roscoe, Schofield, and Thurairajah ( 1 9 6 3 ) w i l l be applied to the data obtained i n this investigation,, Taylor ( 1 9 4 8 ) proposed that the observed discrepancy between the stress-strain curves of loose and dense sand could be explained by considering the work required to change the volume of the sand during shear, and he develop-ed an expression to account for this boundary energy in the direct shear test. Bishop and Eldin ( 1 9 5 3 ) developed a boundary energy correction to be applied to the measured principal stress difference in drained t r i a x i a l tests on sands„ Bishop ( 1 9 5 4 ) presented a theoretical development of this energy correction (here-after referred to as the Bishop correction) in which i t was shown that the correction was valid only at failure (when the major effective principal where e\ m 4 3 axial strain), Hvorslev (1953) suggested that for clays, a significant quantity of energy may be stored or released during drained and undrained shear tests as a result,of induced shearing strains. Thus any attempt to establish an energy equation for clays must recognize this internal energy. It might be noted that during the shear of sands,, i t i s believed that very l i t t l e energy i s released or stored internally and thus a correct energy balance can be obtained by considering the external energy only, Roscoe, Schofield and Wroth (1958) published experimental evidence indicating that, for remolded- clays, good agreement between drained and un-drained t r i a x i a l tests, could be obtained i f Bishop's energy correction was applied to the principal stress difference (a{9 - 03") measured at a l l stages in a drained t r i a x i a l test,- Poorooshasb and Roscoe (1961) indicated that boundary energy corrections do not account for changes in internally stored energy and subsequent development of this concept for an idealized isotropic "wet" clay led to.an energy equation which included terms account-ing for both boundary energy and internally stored energy (Roscoe, Schofield, and Thurairajah, 1963), This equation was believed valid for a l l points along stress paths in both drained and undrained t r i a x i a l tests, Roscoe, Schofield and Thurairajah (1963), working with an idealized isotropic "wet" clay, presented an energy equation which included terms accounting for both boundary energy and internally stored energy, which was valid for a l l points along a stress path, and which was to be applied to both drained and undrained test data, Rowe (1962), working with granular media, established an energy correction to be applied to the.effective confining pressure at a l l stages in the t r i a x i a l test and- showed that his correction was similar to the Bishop correction (Rowe, Barden and-Lee, 1964), Rowe, Oates and Skermer (1963), i n a paper dealing with overconsolidated clays, proposed that the correction derived for granular media could be applied to clays i f volume changes due to changes in mean effective stress were not included in any computations involving volumetric strain, Rowe, Barden and Lee (1964) offered a review of the energy corrections presented up to that data and concluded that, on theoretical grounds, the Bishop energy balance (Bishop, 1954) i s correct, but the Roscoe energy balance (Roscoe, Schofield and Thurairajah, 1963) does not correctly represent the behavior of dilating materialso The theoretical development of each of the above energy balances re-quires the assumption of idealized materials and hence the resulting equa-tions may be expected to only approximately reflect the behavior of real s o i l s . There i s however, limited experimental evidence to support a l l of the corrections proposed (Roscoe, Schofield, and Wroth, 1958, Roscoe, Schofield, and Thurairajah, 1963, Rowe, Gates and Skermer, 1963, and other). In the hope of shedding more light on the range of valid i t y of any or a l l of these corrections, some of the test data obtained in the present research program has been analysed using three of the proposed energy balances. Bishop energy correction The energy correction proposed by Bishop (1954) is given by: <«l' " ° 3 ° ) C O J r r e c t e d " ( O l ' - ° y > O D 8 e r v e d - °3* ^ 0 0 0 , 0 , . o . o o o . ,,(10) Coi0 - 0 3 ' ) » principal stress difference (deviator stress) v • increase in volume per unit volume (volumetric strain) • - ( e j + £2 + £3) °l'f> °V B major and minor effective principal stress respectively e l o c 2 » , e 3 " principal strains (compression positive) As has been mentioned previously, this correction, to be applied to drained tests, i s valid only at failure (Bishop, 1964), In the above form, the correction cannot be used directly to determine a corrected effective angle of shearing resistance, 0 However, Bishop (1964) has shown that, by re-solving the stress system into an ambient stress, 03", and a principal stress difference, (oj° - 03°), an expression for <J>' corrected can be obtained into which Equation (10) may be substituted: Si„ «, for - <*V) „ frl.',„r, ?\) corrected , Y corrected ( o V +03") (ci - 03") corrected + 2o 3 9 0 0 o o o ( l l ) Application of Equations (10) and (11) to the failure condition in the drained tests yielded an average corrected 4>9 of 29,1°, which is in only f a i r agreement with the average <j>* of 30 05° measured at the maximum effec-tive principal stress ratio, (Circs') max0 in the undrained tests e The strains at which the maximum effective principal stress ratio occurred in the drained and undrained tests were widely different 0 In the drained test ( o i ^ J 3 9 ) max, occurred at about 30 percent axial strain whereas in the un-drained test ( a - a 3 5 ) max„ occurred at about 17 percent axial strain. Be-cause the two $"s are based on stress calculations which assume that the sample deforms as a right cylinder choughout the test whereas in fact the sample bulges, perhaps the above lack of agreement can be expected. The Bishop correction i s valid at failure only, and therefore no attempt has been made to investigate the application of the correction to other points along the stress path, Rowe energy correction Rowe (1962) proposed that, in a drained test 0 0*3^  , 8 3 C7 3 ° - ,(1.4* ) 0 0 o 0 fl 0 0 0 o 0 0 o 0 0 o 0 o 0 o 0 0 c o 0 fl 0 o 0 (12) ^ corrected 3 observed VEJ dV where -~r • rate of volumetric strain ci * axial strain rate at a l l stages in the test and that, for clays, o , 8 2 * f 2 C £ * f . r . l i . i n , . . . i m fan (L*> 4- — ± ^ 4- r i,, 1 fan f £ S 4- «£• r * ' 3 - ' V G i *3* (1 + S t ) ^ • tan (45 + ~ ) 4- "^T~ t a n (45 + ) 0 o 0 o o o o , o o o (13) where <^  • interparticle shearing parameter C£ • interparticle cohesion parameter Working with clays Rowe, Oates and Skermer (1963), found i t necessary to modify the dllatancy term to account for the elastic component of volume change which they assumed was due to changes in mean effective stress. However, no method of determining the elastic component of volume change was presented. Experimental evidence showed good agreement with the theory when the clays were reloaded as long as the axial strain did not exceed 0,5 percent, but only f a i r agreement was abserved during the i n i t i a l loading cycle. The authors concluded that the interparticle cohesion term, c f B was zero for normally consolidated clays. In the present test series, the elastic volume change was determined from the elastic rebound curve of Haney clay (Figure 13) and was computed as follows: AeeW C\A\ . -,e S " o o o o o o o o o o o o o , o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o \ L ^ ) AV • — » — — G Y s to where AV • elastic volume change Ae e » change in void ratio attributed to elastic volume change • «K°log^Q(p'/pn°) Wg " weight of solids G ** specific gravity of s o i l grains 8 FIGURE 13. RELATIONSHIP BETWEEN WATER CONTENT AND MEAN EFFECTIVE STRESS FOR TRIAXIAL CONSOLIDATION AND UNLOADING (BACK-DRAINAGE) 4 8 K' • coefficient of expansion* slope of the void ratio versus logarithm of mean effective stress during isotropic unloading • 0,11 for Haney clay p ° • i n i t i a l mean effective stress Thus the rate of volumetric strain used in Equation (12) to compute a correction to 03' becomes: The Rowe energy correction, modified for the assumed elastic volume change was determined for test S-17 and the results are shown graphically in Figure 14, It can be seen that the data indicates a value of c f » 23,3 lbs,/sq, i n , , and <f>£ • 12 02° for an effective confining pressure of 40 lbs,/ sq, i n . No attempt to reload the samples was made. At failure, application of the Rowe energy correction to the drained data yielded an average correct-ed <}>' » 31,5° which, like the Bishop correction, is in only f a i r agreement with the of 30,5° measured at the maximum effective principal stress ratio ( o V / o V ) max, in the undrained tests, Roscoe, Schofield and Thurairajah energy correction The energy equation proposed by Roscoe, Schofield and Thurairajah (1963) i s based on the following assumptions: o 1, The energy recoverable from a unit bulk volume of clay at voids ratio, e, under mean effective stress, p°, i s : U SB Kp* O O O 0 0 O O O O 0 O O O O 0 O 0 0 0 0 0 O O O O O 0 0 O O O O O O 0 O 0 0 (15) e 1+e the increase in recoverable energy when the mean effective stress increases by 6p° i s : 5U O O 0 0 0 0 O O 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O O 0 0 O 0 O (16) e 1+e FIGURE 14. APPLICATION OF THE ROWE ENERGY CORRECTION TO TEST S - 17 2o The rate at which energy is dissipated during shear distortion of unit volume of s o i l when under mean effective stress, p°, iss ^ ^  m Mp o o o o o o o o o b o o o o o o o o o o o o o o o o o o o o o o o ( 1 7 ) where K » a constant " s l o p e of the void ratio versus natural logarithm of mean effective stress » 0,048 for Haney clay U"e = recoverable energy W «• dissipated energy de » 2 / 3 ( 6 e1 - 663) » distortion increment M • a constant Thus the energy equation may be written: ^v dp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CIS) Mw v n * 6e 1+e 6e In equation ( 1 8 ) , the corrected principal stress difference, q w, is assumed equal to a constant, M, times ste mean effective stress, and is seen to consist of three termst the observed principal stress difference, q, the dv boundary energy correction, p' ~ , and the elastic energy correction, K 60' 1+e" ° T h e c o r r e c t * o n * 8 applicable to both drained and undrained normal-ly consolidated t r i a x i a l tests at a l l points along their stress paths 0 Applying the correction to the data of this investigation yields the results shown in Figure 150 It may be seen that, except for the i n i t i a l stages of the tests, the corrected data does approximate a straight line, the slope of which is M «• l 0 2 7 o Using this value of M, a determination of the corrected can be made as follows: On the line q w • Mp °, 3 • . ' CORRECTED DATA •O—o—o— UNCORRECTED DRAINED DATA X * X UNCORRECTED UNDRAINED DATA 0 20 40 60 80 100 120 140 p' ( LBS./ SQ. IN.) F I G U R E 15. A P P L I C A T I O N O F T H E R O S C O E , S C H O F I E L D A N D T H U R A I R A J A H E N E R G Y C O R R E C T I O N T O D R A I N E D A N D U N D R A I N E D T E S T D A T A . Therefore a 1 / 0 3 ' - 1 - -(a^/a^) + Therefore 0 2 / 0 3 ' - ~ ~ » | ™ » 3„20 This value of the effective principal stress ratio yields a corrected <J>° of 3106° which i s in good agreement with the corrected <{>' of 31,5° deter-mined from the Rowe energy correction 0 There is considerable scatter in the-plotted result of data corrected by the Roscoe et a l 0 and Rowe energy corrections (Figures 14 and 15), par-ticularly at low axial strains. Some of the low strain scatter may be attributed to the measured axial strain which i n i t i a l l y may include seat-ing of the porous stones, sample, loading cap and ram. Pore pressures developed during the early stages of a drained test w i l l modify the value of the mean effective stress and no allowance for this has been made. The end restraint offered by the porous stones-prevents volume change occurring uniformly throughout the sample and thus calculated volumetric strains based on the total volume of the sample w i l l be too small (Rowe, 1963)„ The coarseness of the volume change readings (estimated to 0o01 cu, cms0), taken at very small time intervals, w i l l also be reflected in any rate of volume change that i s computed, It may be noted that the assumption that the elastic energy component i s a function of p" only i s open to question, particularly in sensitive clays where large structural changes are believed to occur under deviatoric stresses. It i s concluded that the Roscoe, Schofield and Thurairajah energy correction does permit correlation of drained and undrained behavior throughout the shearing process although considerable experimental scatter i s observed in the early stages of the tests 0 The Bishop and Rowe energy corrections bring the drained and undrained test data into only f a i r agree-53 merit at failure (defined as the maximum effective principal stress r a t i o ) 0 Only limited use of the above energy corrections has been made in subsequent sections of this thesis because none of them can be conclusively shown to be applicable to Haney clay 0 Until further information as to the role of energy corrections in t r i a x i a l tests i s available, i t i s f e l t that no benefit can be derived from the application of energy corrections to the stress-strain curves,, In an attempt to compare the drained and undrained strengths j, however, a l l three energy corrections have been considered be-cause i f indeed the strength developed in t r i a x i a l tests i s independent of test type, then a correct energy balance should indicate t h i s 0 4 o 5 Stress-strain relationships  Drained shear tests The relationships between principal stress difference and axial strain, and between effective principal stress:ratio and axial strain are shown in Figures 16g 1 7 , and 18„ The results of a l l drained tests have been includ-ed in these diagrams0 The maximum principal stress difference and maximum effective principal stress ratio, occur together at approximately 30 percent axial strains Similar, high strains to failure in drained shear tests on sensitive clays have been reported by Crawford ( 1 9 6 1 ) „ A feature of the drained stress-strain curves i s the abrupt change in slope that occurs at about 2 percent axial strain in those samples consoli-dated to an a l l round effective stress of 4 0 lbs<,/sq„ i n 0 This change in slope may also be seen in samples consolidated to higher effective stresses but i t is not so marked in these cases 0 The overall appearance of the stress-strain curves may be crudely likened to that of steel which exhibits zones of elastic, plastic, and strain-hardening deformations 0 However the "plastic deformation" zone i s only v i s i b l e at an effective confining pres-1 54 FIGURE 16. STRESS-STRAIN CURVES FOR T E S T S-17 AXIAL STRAIN (%) FIGURE 17. STRESS-STRAIN CURVES FOR TEST S-16 56 FIGURE 18. STRESS-STRAIN CURVE FOR TEST S-15 sure of 40 lbso/sq 0 i n 0 Similar drained stress-strain curves for sensitive clays have been reported by Crawford (1959)„ At f i r s t i t was believed that the change in slope was not a character-i s t i c of the clay 9 but a fault, of the testing equipment,. To investigate this, a sample of hard.rubber was prepared whose low stress-strain proper-ties were approximately similar to those of the clay 0 The rubber sample was placed in a Baldwin-Hamilton Universal Testing Machine and i t s load-deformation curve obtained 0 The same sample was then placed in the t r i a x i a l apparatus and subjected to a chamber pressure of 50 lbs 0/sq 0 in„ The sam-ple was strained at the same rate as that applied to the clay (0 o5 percent per hour) and the resulting load-deformation curve was recorded,, Figure 19 shows the load-deformation curve of the rubber sample compared to that of a drained test on Haney clay at a chamber pressure of 50 lbs„/sqc i n 0 No change in slope of the rubber load-deformation curve occurred and i t was therefore concluded that the testing: equipment was not at f a u l t 0 Because the rate of testing was-slow (0„5 percent per hour) B i t was thought that the deformation behavior-of the clay may have been influenced by creep and that the sharp change in slope of the stress-strain curve cor-responded to an upper yield stress at which the creep rate increased (Murayama and Shibata 0 1961)0 However, testing at a rate of strain of 2,5 percent per hour (5 times the previous rate) did not substantially modify the curve (see Figure 20) and thus creep does not appear to be directly responsible for the observed behavior„ As has been pointed out, the change in slope.is only marked at the low effective confining pressure (40 lbs 0/sq o i n 0 ) 0 This is very close to the maximum past pressure (38 lbs 0/sq 0 in,) determined from oedometer tests„ Thus there exists the possibility that the sharp change in slope 70 0.00 0.02 0.04 0.06 0.08 0.10 0.12 DEFLECTION (INCHES) FIGURE 19. LOAD-DEFORMATION CURVES FOR RUBBER AND HANEY CLAY. 59 af the stress-strain curve Is a reflection of the past history of the clay. Another possible explanation for the break in slope is associated with the pore pressures developed during the i n i t i a l stages of the tests (Section 4,3), These pore pressures cause temporary increases in the effective prin-cipal stress ratio and thus may influence the deformation characteristics of the clay* If this were the case, samples which developed higher pore pressures (those tested at higher confining pressures and at higher rates of strain) would be expected to develop more pronounced changes in stress-strain slope but this did not occur. It is possible that the change in slope i s a result of structural changes occurring within the sample and i s thus related to the sensitivity of the clay 0 During consolidation, some of the sensitivity may be destroyed and hence at higher consolidation stresses the change in slope would not be as noticeable. This can be seen in Figures 17 and 18, Investigations into the creep of clays (Murayama and Shibata, 1961) have shown that significant rates of strain occur under small constant principal stress differences. It is reasonable to assume, therefore, that although creep was not responsible for the change in slope referred to above, the overall deformation.characteristics of the s o i l were affected by the creep strain occurring during the 60 hours of testing. However, test S-10 (Figure 20), tested at an applied axial strain rate of 2,5 percent per hour, did not f a l l at a lower axial strain thus indicating the influence of creep was small. Some clays are known to exhibit increases in strength attributed to thixotropy. Because a sensitive clay undergoes substantial remolding dur-ing shearing, i t i s believed that some thixotroplc strength increase is l i k e l y to occur. No attempt was made to determine the fchixotropic proper-ties or creep behavior of Haney clay, Undrained shear tests The most notable feature of the drained shear tests i f the different strains at which the maximum principal stress difference and maximum effec-tive principal stress ratio occur 0 Figures- 21, 22, and 23 show the rela-tionship between principal stress.difference and axial strain and between effective princiapl stress ratio and axial strain during undrained tests. It may be seen that the maximum principal stress difference occurs at approximately 3 percent axial strain, whereas the maximum.effective p r i n c i -pal stress ratio occurs at approximately 17 percent axial strain, neither of which compare with the drained failure strain of 30 percent 0 Kenney (1959) presented experimental evidence indicating that the degree of mobil-ization of <f>s at (ox" ~ a 3°) maxois related to the sensitivity of the s o i l 0 This relationship i s shown in Figure 24 where the degree of mobilization of 4>° i s expressed as ^ *^g^""^f""^^*,"~ "'^ ^ m a*° Haney clay, with a sensitivity tan 24 5° of 12 has a degree of mobilization of $8 » 1 •',0 -o. • 0,77, and this value is seen to l i e f a i r l y close to the line proposed by Kenney, It should be noted that i f creep and thixotropic effects are present during drained shear tests, they are also l i k e l y to influence the undrained deformation characteristics of the clay. As mentioned earlier, no study of these phenomena was undertaken. 4.6 Shear strength As implied earlier in this report, the shear strength of a s o i l i s usually defined by the failure c r i t e r i a of maximum principal stress d i f f e r -ence, ( a j 8 = C3')max,, or maximum effective principal stress ratio, (°l ' / ° 3 8 ) i n a x < ' Occasionally, the shear strength is quoted as the strength developed at some particular strain. A l l three c r i t e r i a will be discussed 0 6-10 15 2 0 25 0.0 3 0 AXIAL STRAIN (%) FIGURE 21. STRESS-STRAIN CURVES FOR TEST C-U-l 6 4 0 *- 0.0 10 15 20 25 30 AXIAL STRAIN (%) FIGURE 23. STRESS-STRAIN CURVES FOR TEST C-U-7 FIGURE 24. RELATIONSHIP BETWEEN NATURAL SENSITIVITY AND DEGREE OF MOBILIZATION OF d j ' AT (<"•,'- 0-3 ) m f l X . (After T.C. KENNEY, 1959) in the following paragraphs, with particular attention being directed to-ward a comparison of drained and undrained strength. The results are shown in the form of plots of 1/2(ai' - 0 3 ' ) versus 1/2(oj' + o 3 9) at failure. Thus i f a is the angle of slope of the best Btraight line drawn through such points, i t can be shown that sin <t>" • tan a where <J>" is the effective angle of shearing resistance. The un-corrected drained and undrained envelopes for the-(oj' - o^^max, failure criterion are shown in Figure 25, and for the (o\0/c3')maxo failure c r i t e r -ion i n Figure 26, Figure 27 shows the uncorrected undrained envelope, (oi ' / o3')max,, and the drained envelope, (ay'/o3')max0 corrected for volume change using the energy corrections presented in Section 4,4, As reported in Section 4,4 only f a i r agreement is obtained between drained and undrained strength at (01'/o^'lmax, i f the Bishop or Rowe energy corrections are applied to the drained data. This may be seen in Figure 27 in which the undrained <f> " i s 30,5° and the corrected drained 4>'s are 29,1° (Bishop) and 31,5° (Rowe), The <J>" obtained using the Roscoe, Schofield and Thurairajah energy correction is seen to l i e slightly above these, having a value of 31,6°, Henkel (1960), working with remolded clays, reported good agreement between uncorrected drained and undrained strengths at (cy' - 0 3°)max. but pointed out that the same correlation would not be expected in undisturbed sensitive clays due to the important effect of structure. Reference to Figure 25 shows that the undrained <J>° •» 24,5° and that the uncorrected drained » 28,1° thus no agreement does exist for Haney clay at ( c i ' - 0 3 ' ) max, Roscoe, Schofield and Wroth (1958) proposed a c r i t i c a l void ratio (CVR) for remolded clays which represented an ultimate state for the clay 0 In this state, continuous yield would occur at constant void r a t i o 0 The CVR (LBS. / SQ. IN.) FIGURE 27. CORRECTED MAXIMUM EFFECTIVE PRINCIPAL STRESS RATIO FAILURE ENVELOPES. line was believed to be independent. of stress path. Figure 28 shows that during a drained test, the volume decreases continuously and Figure 29 shows that during an undrained. test the-pore pressure increases continuously, even after f a i l u r e 0 Thus a c r i t i c a l state for Haney clay was not reached during this test series. However, the flattening slopes of Figures 28 and 29 i n -dicate that a c r i t i c a l state may exist at strains greater than those applied in this investigationo It has been widely reported (Taylor, 1948, Roscoe, Schofield and Wroth, 1958, Henkel, 1960, Hvorslev, 1960) that, for remolded and some insensitive undisturbed saturated, normally consolidated clays, there is a relationship between the strength.and the water content of a specimen (at the maximum principal.stress difference) that i s independent of stress path. This relationship i s shown in Figure 30, Figure 31 i s a plot of water content versus various stresses for the cases of isotropic consolida-tion, drained failure and undrained failure; again both failure c r i t e r i a are included. It may be seen that the normal consolidation curve for the drained (Hirst) and undrained (Byrne) test series, although approximately parallel, do not coincide Although this attests to the variable nature of Haney clay, i t is believed that the variation i s not large enough to i n v a l i -date comparisons of drained and undrained strengths. The test results do not permit a direct comparison of the strengths (at the maximum principal stress difference) for any given water content because the water contents of the drained and undrained tests do not overlap. However i t can be seen that, because the graph of strength (represented by (o^ * - 0"36)max, or 0 3 ' at failure) for the undrained tests does not l i e on a projection of the graph of strength for the drained tests, the strength at any water content i s not independent of stress path. If, for i l l u s t r a t i o n purposes, extra-69 0 5 10 15 20 25 30 AXIAL STRAIN (%) FIGURE 28. RELATIONSHIP BETWEEN WATER CONTENT AND AXIAL STRAIN IN A DRAINED TEST. 70 6 0 o Q. 15 •> 10 * 1 1 1 1 1 L -0 5 10 15 20 25 30 AXIAL STRAIN (%) FIGURE 29. RELATIONSHIP BETWEEN PORE PRESSURE AND AXIAL STRAIN IN AN UNDRAINED TEST. VARIOUS STRESSES (LOGARITHMIC SCALE ) FIGURE 30. TYPICAL WATER CONTENT - STRESS RELATIONSHIP FOR SATURATED, NORMALLY CONSOLIDATED REMOLDED AND INSENSITIVE CLAYS. 72 FIGURE 31. RELATIONSHIP BETWEEN WATER CONTENT AND STRESS AFTER NORMAL CONSOLIDATION AND AT (cr, - oV ) m a x AND (o-; /a-') FAILURE CRITERIA. o n . 1 ° max. 73 p o l a t i o n of the data i s accepted (shown dotted i n Figure 31), i t may be seen that at a water content of 30 percent, the maximum p r i n c i p a l s t r e s s d i f f e r -ence i s 63 l b s , / s q , i n , i n the undrained t e s t s and i s 51 l b s , / s q , i n , i n the drained t e s t s . For the maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o n f a i l -ure c r i t e r i o n , a s i m i l a r l a c k of agreement i s apparent. For example, at a water content of 30 percent, 0 3 ' « 32 l b s , / s q , i n , i n the undrained t e s t s and 28 l b s , / s q , i n , i n the drained t e s t s . I t has a l s o been reported ( T a y l o r , 1948, Roscoe, S c h o f i e l d and Wroth, 1958, Henkel, 1960, Hvorslev, 1960) that the change i n water content during drained shear t e s t s on normally c o n s o l i -dated samples i s independent of the i n i t i a l water content, that i s , the l i n e r e p r e s e n t i n g f a i l u r e , (oV - o3')max,, i s p a r a l l e l t o the normal con-s o l i d a t i o n curve (Figure.30), Reference t o Figure 31 shows that none of the curves are p a r a l l e l to the normal c o n s o l i d a t i o n curve and thus the change i n water content during drained shear i s not independent of i t s i n i t i a l v a l u e . I t may t h e r e f o r e be concluded that the st r e n g t h - v o i d r a t i o r e l a t i o n s h i p s developed f o r remolded c l a y s are not a p p l i c a b l e to undisturbed e x t r a - s e n s i t i v e c l a y s . T h i s c o n c l u s i o n i s not new but was i m p l i e d by Taylor (1948), Henkel (1960), and Hvorslev (1960), Figure 32 shows the v a r i a t i o n of a x i a l s t r a i n w i t h uncorrected drained and undrained s t r e n g t h . I t can be seen t h a t the st r e n g t h (which i s i n terms of <(>') i s very n o t i c e a b l y a f u n c t i o n of both f a i l u r e c r i t e r i o n (whether i t be ( o V - 03°) ( f l i V o V ) , or s t r a i n ) and type of t e s t , Ttl£LX 0 TI1£IX o The v a r i a t i o n of st r e n g t h w i t h f a i l u r e c r i t e r i a may a l s o be seen i n Figures 25 and 26, At the maximum p r i n c i p a l s t r e s s d i f f e r e n c e , the uncorrected drained s t r e n g t h (<J>' • 28,1°) i s gr e a t e r than the undrained s t r e n g t h ($' - 24 05°) whereas at the maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o , the uncorrected drained s t r e n g t h ($' • 28,1°) i s l e s s than the undrained FIGURE 32. VARIATION OF THE MOBILIZED EFFECTIVE ANGLE OF SHEARING RESISTANCE WITH AXIAL STRAIN. strength • 30,5°), Thus from a practical point of view, the choice of a factor of safety in any problem concerned with sensitive clay becomes d i f f i c u l t because both type of failure (drained or undrained) and failure criterion must be considered,, Also, the strains required to develop the (oV - 03 ') and ( o 1 ' / / 0 3 ° ) „ failure c r i t e r i a can be quite large and therefore a definition of failure i n sensitive clays must recognize not only the strength, but also the strain required to develop that strength, and the drainage conditions presents In Section 4,5 i t was stated that thixotropic strength gain probably influenced the stress-strain characteristics of the clay tested. It was also pointed out that the confining pressure to which the sample was i n i t i a l -ly consolidated caused structural adjustments to occur within the clay and thus perhaps reduced i t s sensitivity. Evidence to support this can be found in Figures 16, 17, and 18 where i t can be seen that the axial strain to failure decreased slightly at the higher consolidation pressures. This de-crease infers that the structure is less sensitive because, in general, soils with low sensitivities f a i l at lower axial strains than those with high sen-s i t i v i t i e s (Bishop and Henkel,. 1962), The strength of the sample in test S-10 (Table IV) was very similar to those samples tested at the slower rate of strain which indicated that, with-in the limits investigated, the rate of strain does not significantly i n -fluence the measured strength. No attempt was made to investigate the effect of sample disturbance on the measured properties of the clay. Every precaution was taken to ensure that minimum disturbance occurred and i t i s believed that the strengths quoted above are representative of the undisturbed material. 76 4,7 Summary I t i s appreciated that the number of tests conducted i n t h i s i n v e s t i -gation was smallo However0 the consistency of the results obtained i s an encouraging indication of t h e i r v a l i d i t y . The o v e r a l l behavior of the clay tested i s sim i l a r to that reported by Crawford (1959, 1961) who has conduct-ed extensive t r i a x i a l shear tests on sensitive clays. The s i g n i f i c a n t difference i n the s t r e s s - s t r a i n characteristics of drained and undrained t r i a x i a l compression tests on ah extra-sensitive clay i s perhaps the most important feature observed i n t h i s investigation, and points to the i n f l u -ence that structure has on the s o i l behavior. The fact that the strength of an extra-sensitive clay i s very dependent on the f a i l u r e c r i t e r i a used to define the strength, and on the drainage conditions present, must not be overlooked i n any extrapolation of laboratory data to f i e l d conditions. i 77 CHAPTER 5 CONCLUSIONS The purpose of the present study has been to investigate the stress-strain behavior of an undisturbed extra-sensitive clay during t r i a x i a l coin-pressiono The following conclusions are based on the results of a limited number of tests on one clay, and hence extrapolation of some of these con-clusions should be avoided u n t i l further data on clays of other s e n s i t i v i -ties i s availableo 10 The sensitivity of a clay, which i s a measure of the sta b i l i t y of i t s i n i t i a l structure, i s of primary importance in determining i t s stress-strain behavioro 2 0 A relationship between void ratio and strength, which i s inde-pendent of stress path, visualized by Taylor ( 1 9 4 8 ) , Hvorslev ( 1 9 6 0 ) and others for remolded and insensitive undisturbed normally consolidated, saturated clays, does not exist for an undisturbed extra-sensitive clay D 3o A failure envelope (failure being defined at the maximum pr i n c i -pal stress difference), independent of stress path, which was suggested by Henkel ( 1 9 6 0 ) for remolded clays does not exist for an undisturbed extra-sensitive clay„ 4 0 A c r i t i c a l void ratio (Roscoe, Schofield and'Wroth, 1 9 5 8 ) at which a s o i l yields continuously at constant, volume during drained shear was not reached during this test series, although the available evidence indicates that i t may exist at strains greater than those investigated. 5o The strength of an extra-sensitive clay at the maximum effective principal stress ratio i s not independent of test type i f the Bishop ( 1 9 5 4 ) or Rowe ( 1 9 6 2 ) energy corrections are applied to the drained test data. For Haney clay, Bishop <j>° corrected » 2 9 . 1 ° , Rowe <J>5 corrected » 3 1 0 5 ° , undrained $*^m 30,5°,, 6 0 The Roscoe, Schofield and Thurairajah (1963) energy equation, when applied to the drained and undrained test data, does yield an approxi-mately constant value for the slope of the q w versus p" curve, M » 1,27, The corrected angle of shearing resistance, determined-from M($' - 31 06°) is approximately the same as that obtained from the drained data corrected by the Rowe (1962) energy correction • 31,5°), 7 0 The uncorrected effective angle of mobilized shearing resistance, does not only vary widely with axial strain, but i s also a function of the drainage conditions during shear, and of the criterion of failure that i s usedo 8, Because of the large strains involved, and because of the i n -fluence of drainage conditions, the generally accepted failure c r i t e r i a of maximum principal stress difference-and maximum effective principal stress ratio are not satisfactory for an extra-sensitive clay, 9a In drained shear tests on an extra-sensitive clay, the strain at which failure occurs appears to decrease with an increase in the consolida-tion stress, 100 Calculations indicated that significant pore pressures may develop at low strains in drained tests, l l o For the clay tested, rates of strain between 0 05 percent and 2,5 percent per hour do not significantly affect the strength or stress-strain behavior of 2,8 ins, by 1,4 ins, diameter t r i a x i a l samples. CHAPTER 6 SUGGESTIONS FOR FURTHER RESEARCH Since the number of t r i a x i a l tests-performed in this investigation was small, i t i s suggested that further tests of a similar nature be per-formed on other sensitive clays to establish i f the conclusions drawn from this test series are applicable to a l l sensitive clays. Following i s a l i s t of areas of investigation that have been suggested by the present research program. Also included are recommenda-tions for improved testing equipment, 1, Tests on larger samples of clay w i l l reduce the effects of sample disturbance and also permit a more representative sample of clay to be tested. This i s particularly necessary when investigating highly laminated material such as Haney clay. Because sensitive clay does not f a i l u n t i l high axial strains have developed, the use of frictionless end platens (Rowe and Barden, 1964) w i l l significantly increase the uniformity of stresses within the sample and improve the validity of stress calculations which rely on the assumption that the s o i l deforms as a right cylinder (Olson, 1962), 2, In remolded saturated clays, the existence of a relationship between strength and water content at failure that i s independent of stress path i s widely recognised (Roscoe, Schofield and Wroth, 1958, Hvorslev, 1960, Scott, 1962), It has been shown that such a relationship i s not pre-sent in an undisturbed extra-sensitive clay, but no investigation of the remolded properties of this clay has been undertaken. It i s therefore suggested that the remolded properties of Haney clay be determined, 3, Although their existence i s accepted (Hvorslev, 1960), the development of pore pressures during drained tests has received l i t t l e attentiono Before pore pressures can be accurately calculated, determina-tions of the values of A and c^ during drained shear must be made. Alterna-tively, the pore pressure may be measured through a probe inserted at the mid-height of the sample, and a distribution of pore pressure within the sample assumed. If drainage i s permitted through the base,only, the pore pressure may be measured at the top stone. El e c t r i c a l pressure transducers of low compliance are believed to be the most satisfactory method presently available of measuring pore pressures, 4, It has been suggested that the effective confining pressure i n -fluences the strain at which failure occurs i n drained tests, A possible explanation for this i s that consolidation tends to destroy the sensitivity of the material by causing structural re-arrangements within the sample. Further investigation of this effect in both drained and undrained tests is necessary before any definite conclusions may be drawn, 5, The sharp change in the slope of the stress-strain curve of an extra-sensitive clay during drained shear has been reported by Crawford (1959) and in the thesis. Possible explanations for this irregularity i n -clude the influence of past history, residual pore pressures, structure, and creep. Perhaps further investigation of the stress-strain behavior of extra-sensitive clay might indicate which of the above factors, i f any, are responsible for the observed phenomenon, 6, It is generally accepted that the strength of clay and the shape of i t s stress-strain curve i s affected by the rate of strain applied to the sample (Whitman, I960), However, the.limited test' data reported herein indicates that, within the range investigated, strain rate has l i t t l e effect on the resulting behavior of an extra-sensitive clay. This suggests that an investigation of the effects of a large range of strain rates on the behavior of extra-sensitive clay is desirable. Such an investigation could report on the effect of strain rate on thixotropic strength gain, creep, develop-ment of pore pressures during drained tests, and equalization of pore pres-sures during undrained tests, 7, An attempt to determine the type of structure which exists in a clay at a l l points along its stress-path would undoubtably furnish a better understanding of the contribution that structure makes to the behavior of the clay, A series of identical tests could be stopped at various points along the stress paths, and the structure determined at each.point by x-ray diffraction technique or electron microscope. NOMENCLATURE Pore pressure coefficient reflecting the dilatancy of the sample Coefficient of compressibility Pore pressure coefficient reflecting the degree of saturation present in the sample slope of water content versus logarithm of mean effective stress during isotropic unloading interparticle cohesion parameter coefficient of consolidation one-half sample height void ratio specific gravity of s o i l solids permeability slope of void ratio versus natural logarithm of mean effective stress during isotropic unloading slope of void ratio versus logarithm to the base 10 of mean effective stress during isotropic unloading A constant mean effective stress » q1 * i n i t i a l mean effective stress observed principal stress difference • (aj' - 03') corrected principal stress difference sensitivity time time to 90 percent consolidation time factor average degree of consolidation Ufi - recoverable energy u - pore pressure u i - i n i t i a l pore pressure v - volumetric strain W - dissipated energy Wg - weight of solids at - water content 8 - depth from surface of clay layer a » slope of l / 2 ( c i ' - o 3') versus l/2( o i ' + 0 3 ' ) failure envelope e Ae - change in void ratio attributed to elastic volume change Au - change in pore pressure Ao^(i»la3) - change in major or minor total principal stress respectively AV - elastic volume change - unit weight of water 6e - 2/3(6ei - 663) » distortion increment e^(i»l,3) - major or minor strain respectively li - rate of axial strain 41' - effective angle of shearing resistance interparticle shearing parameter a - total stress a' - effective stress o^(i"lt3) - major or minor total principal stress respectively o^'(i"l e3) - major or minor effective principal stress respectively al'/aS* ~ effective principal stress ratio (°1 - O j ) - principal stress difference (deviator stress)" ( 0 1 ' - 0 3 ' ) o c' - effective confining stress » 0 3 9 dV - rate of total volumetric strain V •e dV - rate of elastic volumetric strain 84 LIST OF REFERENCES AMERICAN SOCIETY OF CIVIL ENGINEERS , 1962, "Nomenclature for s o i l mechanics," Proc, Am, Soc, Civ, Eng., SMF Div,, Vol, 88, No, SM3, pp, 185-188, ARMSTRONG, J,E,, 1957, " S u r f i c i a l Geology of New Westminster map-area, B r i t i s h Columbia," Geological Survey of Canada Paper 57-5, 25 pp, BISHOP, A,W0, and A,K,G, ELDIN, 1953, "The effect of stress history on the r e l a t i o n between <J> and porosity of sand," Proc, 3rd, Int, Conf, S o i l Mech,, Vol, 1, pp, 100-105, BISHOP, A , W o , 1954, Correspondence on a paper by A,D,M, Penman, Geotechnique, Vol, 4, pp, 43-45, BISHOP, A o W , , and D,J, HENKEL, 19620 "The Measurement of S o i l Proper-t i e s i n the T r i a x i a l Tests," Edward Arnold Ltd,, 200 pp, BISHOP, A , W o , 1964, Correspondence on paper by P,W„ Rowe, L, Barden, and I,K, Lee, Geotechnique, Vol, 14, pp, 370-371, BYRNE, P,M,, 1966, "Effective stress paths i n a sensitive clay," M,A,Sc, thesis, University of B r i t i s h Columbia, Vancouver, Canada, (Typewritten), CRAWFORD, C B o , 1959, "The influence of rate of s t r a i n on e f f e c t i v e stresses i n sensitive clay," ASTM Spec, Tech, Publ, No, 254, pp, 36-48, CRAWFORD, C.B,, 1961, "The influence of s t r a i n on shearing resistance of sensitive clay," ASTM P r o c , Vol, 61, pp, 1250-1265. GRIM, R,E,, 1953, "Clay Mineralogy," McGraw-Hill Book Company, Inc, 380 pp, HENKEL, D,J,, and G,D, GILBERT, 1952, "The effect of the rubber membrane on the measured t r i a x i a l compression strength of clay," Geotechnique, Vol, 3, pp, 20-29, HENKEL, D.J,, 1960, "The shear strength of saturated remoulded clays," Proc, Am. Soc, Civ, Eng,, Research Conference on Shear Strength of Cohes-ive S o i l s , pp, 533-554, HENKEL, D,J., and V,A. SOWA, 1963, "The Influence of stress history on stress paths i n undrained t r i a x i a l tests on clay," ASTM Spec. Tech, Publ, No. 361, pp, 280-291, HVORSLEV, M„J„, 1953, Discussion on s o i l properties, Proc, 3rd, Int, Conf, S o i l Mech,, Vol, 3, pp, 122-124, HVORSLEV, M,J,, 1960, "Physical components of the shear strength of saturated clays," Proc, Am, Soc, Civ, Eng,, Research-Conference on Shear Strength of Cohesive S o i l s , pp, 169-273, 85 KENNEY, T.C, 1 9 5 9 o D i s c u s s i o n on paper by C.B, Crawford. ASTM Spec. Tech, P u b l , No, 254, pp, 49-58, LAMBE, T , W , , 1958, " S o i l T e s t i n g f o r Engineers," John Wiley and Sons, Inc., 150 pp, LAMBE, T.W,, 1958a. "The s t r u c t u r e of compacted c l a y , " Proc, Am, Soc, Ci v , Eng,, SMF Div , , V o l . 84, No, SM2, Paper 1654, 34 pp, LAMBE, T,W,, 1958b, "The engineering behavior of compacted c l a y , " Proc. Am, Soc. C i v , Eng,, SMF Div , , V o l , 84, No, SM2, Paper 1655, 35 pp, LEONARDS, G,A,, 1962, Chapter 2 of "Foundation Engineering," McGraw-Hill Book Company, Inc. 1100 pp, MURAYAMA, S,, and T, SHIBATA, 1961. " R h e o l o g i c a l p r o p e r t i e s of c l a y s , " Proc, 5th, I n t , Conf, S o i l Mech,, V o l , 1, pp, 269-273. OLSON, R.E,, 1962, Correspondence on a paper by J.E,B, Jennings and J,B, Burland, Geotechnique, V o l , 12, pp, 355-358, POOROOSHASB, H.B,, and K.H, ROSCOE, 1961, "The c o r r e l a t i o n of the r e -s u l t s of shear t e s t s w i t h v a r y i n g degrees of d i l a t i o n , " Proc. 5th I n t . Conf, S o i l Mech,, V o l , 1, pp, 297-304, POULOS, S . J o , 1964, "Report on c o n t r o l of leakage i n the t r i a x i a l t e s t , " Harvard S o i l Mechanics S e r i e s No, 71, Cambridge, Mass., 230 pp, ROSENQVIST, I , TH,, 1952, "Considerations on the s e n s i t i v i t y of Norwegian q u i c k - c l a y s , " Geotechnique, V o l , 3, pp, 195-200, ROSCOE, K.H,, A,N, SCHOFIELD, and C P , WROTH, 1958. "On the y i e l d i n g of s o i l s , " Geotechnique, V o l , 8, pp, 22-53, ROSCOE, K„H,, A,N, SCHOFIELD, and A. THURAIRAJAH, 1963, " Y i e l d i n g of c l a y s i n s t a t e s wetter than c r i t i c a l , " Geotechnique, V o l , 13, pp, 211-240, ROWE, P , W o , 1962, "The s t r e s s - d i l a t a n c y r e l a t i o n f o r s t a t i c e q u i l i b r i u m of an assembly of p a r t i c l e s i n c o n t a c t , " Proc. Roy, Soc. A, V o l , 269, pp, 500-527, ROWE, P o W , , D,B, OATES and N.A. SKERMER, 1963. "The s t r e s s - d i l a n t a n c y performance of two c l a y s , " ASTM Spec, Tech, P u b l , No, 361, pp, 134-143, ROWE, P.Wo, 1963, D i s c u s s i o n on paper by R,C, H i r s c h f e l d and S,J, Poulos, ASTM Spec, Tech, P u b l , No, 361, pp, 340. ROWE, P.W„, and L, BARDEN, 1964, "Importance of f r e e ends i n t r i a x i a l t e s t i n g , " P r o c , Am, S o c C i v , Eng., SMF Div , , V o l , 90, No, SMI, pp. 1-27, ROWE 9 P,W,, L, BARDEN, and I.K. LEE, 1964, "Energy components during the t r i a x i a l c e l l and d i r e c t shear t e s t s , " Geotechnique, V o l . 14, pp. 247-261, 86 SCOTT, R,F„, 1962 0 " P r i n c i p l e s of S o i l MechaniCBo" Addison-Wesley P u b l i s h i n g Company, I n c , 500 pp 0 SEED, H.B,, J.K. MITCHELL, and C.K. CHAN, 1960. "The stre n g t h of compacted cohesive s o i l s . " Proc. Am. Soc. C i v . Eng 0, Research Conference on Shear Strength of Cohesive S o i l s , pp. 877-964. SKEMPTON, A.W., and R.D. NORTHEY, 1952, "The s e n s i t i v i t y of c l a y s . " Geotechnique, V o l . 3, pp. 30-53. SKEMPTON, A.W., 1954. "The pore pressure c o e f f i c i e n t s A and B." Geotechnique, V o l . 4, pp. 143-147, SKEMPTON, A.W., and L, BJERRUM, 1957. "A c o n t r i b u t i o n t o the s e t t l e -ment a n a l y s i s of foundations on c l a y , 1 ' Geotechnique, V o l . 7, pp, 168-178, TAxL0R, D,W„, 1948, "Fundamentals of S o i l Mechanics," John Wiley and Sons, Inc., 700 pp, TERZAGHI, K,, 1923, "Die Berechnung der D u r c h l ' a s s i g k e i t s z i f f e r des Tones aus dem V e r l a u f der, hydrodynamishen Spannungserscheinungen," S i t z b e r , Akad, Wissen, Wien Math-Natur K l , Abt, H a , V o l , 132, pp. 105-124. TERZAGHI, K,, 1925, "Erdbaumechanik auf bodenphysik-alischer Grundlage," L e i p z i g s D e u t i c k e , pp, 140, TERZAGHI, K,, 1944, "Ends and means i n s o i l mechanics," Engineering J o u r n a l (Canada),, V o l , 27, pp, 608, WHITMAN, R,V,, 1960. "Some c o n s i d e r a t i o n s and data regarding the shear s t r e n g t h of c l a y . " Proc. Am, Soc, C i v , Eng,, Research Conference on Shear Strength of Cohesive S o i l s , pp, 581-614, 87 APPENDIX 88 TRIAXIAL COMPRESSION TEST Sheet 1 of 2 SOIL SAMPLE: Haney Cla\ SPECIFIC GRAVITY J 2 080 TEST TYPES Drained BEFORE TESTS WATER CONTENTS TEST NOoS 17 DATES June 12 t 1965 TESTED BYs T 0 J 0Ho Specimen L o c a t i o n Side Side Side Side Top Bottom Container No 0 H ~ l H-2 H-3 H-4 H-5 H-6 Wt0 Container & Wet S o i l i n emn 57o80 58088 71o32 61096 42070 47o70 Wto Container & Dry S o i l i n gm0 46063 47o22 56019 49D27 35o60 38071 Wto Water i n gm0 U o l 7 Uo66 15013 12069 7ol0 8099 Wto Container In sma 18o99 18061 19o21 18030 18o70 18057 WtoDry S o i l i n gm 27o64 j 28061 36o98 30o97 16o90 20o14 Water Content |4004 | 4008 40o9 41o0 4200 4406 CircumoCMn DiamoCMc Area CM2 Top llo30 3o60 A^ ." 10 018 Center Ho27 3o59 A - 10 o12 c Bottom Uo24 3 058 A ^ 10 o07 Average Water Content, to » 40 08% 7ol0 + 7„10 + 7ol0 + 7nl0 2A Length Wto Wet Sample and Container Wto Container I n i t i a l Wto Wet Sample, W AFTER TESTS WATER CONTENTS 135o70 GM0 .3 o 36_ GM0  132o34 GMo - 7ol0 CM0 Area <• t + c + 10ol2 CMo' Specimen L o c a t i o n Whole Container No 0 H-2 WtoContainer & Wet S o i l i n gm0 199o18 WtoContainer & Dry S o i l i n em„ 169„69 Wto Water i n gm0 29„49 Wto Container i n gm0 76o01 Wt.Dry S o i l i n gm0 93o68 Water Content 31 o 5% Volume drained d u r i n g Volume drained d u r i n g Volume back d r a i n e d T o t a l Volume Change • c o n s o l i d a t i o n shear AV => 2o75"CM0: - 9 031 CM0: • 8085 CM," V, AV » 63o07 CM, | e. V 0o879 89 Sheet 2 of 2 TRIAXIAL COMPRESSION TEST (CONTINUED) MEASURED DIMENSIONS Clrcum0CMo DiamoCMc Area CM Top 11.55 "5,68 A_- 10,64 Center 13o58 4032 A - 14,66 Bottom llo65 3,71 Af» 10,81 T i U 4.90 + 4.90 + 4.90 + 4,90 4.90 CM. Length * 1 1 ' r • r M i 1 n •ir^- • Area » t + 12.69 CM, V f - 62,18 CM Remarks 8 Test #11-16 out ofi one block of clay Teat #17 taken from new block. Alignment f a i r . D i s t i l l e d Water Supply Tank sprung leak under vacuum. Traced to valve stem and fixed TRIAXIAL COMPRESSION TEST APPLICATION OF CHAMBER PRESSURE NO DRAINAGE Chamber Pressure • 5 0 » 0 P 0S 0 I o Test No„ s 17 Back Pressure « 1 0 0 0 P 0 S 0 I 0 Tested bys T 0 J o H 0 D/\TE T I M E HRS. T E M R ° c CHAMBER PR. GuflGE P.S.I. P R E S S . Co«R. P.S.I. Ct4flM8EA PRESSuRt P.S.I. PORE PR. P.S.I. PKESS. CoAR. P.S.I. Pofte P.S.I. S KEMPT* B June 12 /65 l i s 25 24 o0 15o0 • .2 0 2 1 2 0 8 1 4 0 9 - 4 0 2 10o7 9o8 9 0 9 l o O l 118 29 2 5 o 0 -2 04 2 2 0 6 2 4 0 8 - 4 0 2 2 0 o 6 9 0 9 9o9 loOO l i s 35 3 5 0 0 - 2 0 5 3 2 0 5 3 4 0 8 - 4 0 3 30 05 1 0 0 0 10o0 loOO 118 40 4 5 0 0 - 2 0 5 4 2 0 5 4 4 0 8 - 4 o 3 4 0 o 5 7o5 7<,5 l o 0 0 lls45 2 4 o l 5 2 „ 5 - 2 0 5 5 0 0 0 5 2 0 4 »4 0 4 4 8 o 0 Remarks: Regulation good0 T R I A X I A L C O N S O L I D A T I O N C H A M B E R P R E S S U R E G A U G E » 5 2 , 5 P , S , I , T E S T N 0 0 17 G A U G E C O R R E C T I O N » -1.1 P 0 S „ I 0 T E S T E D B Y 8 T 0 J , H , E L E V A T I O N C O R R E C T I O N » -104 P o S , ! , A V G E 0 I N I T I A L W A T E R C O N T E N T C H A M B E R P R E S S U R E - 5 0 o 0 P 0 S 0 I o W E I G H T D R Y S O I L , W g - 93099 G M S B A C K P R E S S U R E » 1 0 o Q P 0 S 0 I 0 W E I G H T W A T E R 8 W » 3 8 0 3 5 G M S D A T E T I M E H R S - M W E L A P S E D T I M £ M M . / E L A P S E D V T I M E B U R E T T E C M . 3 VERTiCfl L D I A L INS. T E M P . °C June 12g 1965 1 1 S 5 5 OsOO O o O O IOOOO 1,0000 24 i l 0?04 0,25 9„90 0sl5 0»50 9 o 8 4 0s34 0075 9078 1§00 1,00 9„70 ls34 1025 9 o 6 0 2tl5 1050 9,52 3s04 1075 9648 4s00 2o00 9o40 6sl5 2,50 9022 9 5 0 0 3o00 9,10 12 s 15 3050 8093 16 s 00 4o00 8o80 20 s 15 4050 80 66 2 5 s 00 5 o 0 0 8,51 30 s 15 5 o 5 0 8,41 36 8 00 6,00 8 o 3 2 42sl5 6,50 8,25 49s00 7,00 8 0 1 9 56 s 15 7 c 5 0 8 , 1 1 0,9680 24,2 61s 00 8000 June 13, 1965 10s08 7,29 0,9652 23,0 11* 55 r - 7,25 0„9645 24,0 A V - 2o.75 CM,3 After consolidation, weight of water » Ww - A V » 3 5 , 6 0 G M S , Water Content « 3 7 , 9 % Remarks 92 TRIAXIAL COMPRESSION TEST , , „ ' Sheet 1 of 3 TEST" TYPE 8 Drained TEST N 0 o j 17 TEST RATES 0 o 0 1 4 Ins,/Hr, TESTED BYs T 0J 0H 0 PROVING RING N O , s 3 2 8 2 BACK PRESSURE - 1 0 7 1 FT,Hg, - 1 0 , 0 P.S d o CALIBRATION FACTOR » 0 . 3 1 6 5 LBS0/DIV0 CHAMBER PRESSURE GAUGE - 52 , .5 P . S o I o LOADS > 1 5 6 LBS, - 0 o 7 6 7 8 LBS0/DIV0 GAUGE CORRECTION * - 1 . 1 P o S . I o INITIAL READING PROVING RING - 2 9 . 6 DIV. ELEVATION CORRECTION - - 1 , 4 P 0 S a I o CONSOLIDATED AREA » 1 , 5 2 9 IN, 2 CHAMBER PRESSURE - . 5 0 , 0 P ' o S . I . CONSOLIDATED LENGTH » 2 o 7 6 0 IN, CONSOLIDATED WATER CONTENT - 3 7 . 9 % D A T E T I M E HRSo V E R T o D I A L I N C H E S PROVo D I A L 0 , 0 0 0 1 I N S , B U R E T T E • C M , 3 T E M P ° C June 1 3 , 1 9 6 5 H o 92 0 o 9 6 4 5 2 9 , 6 1 0 , 0 0 2 4 , 0 1 2 0 1 5 O o 9 6 3 1 4 9 , 5 9 , 9 8 2 4 , 0 1 2 0 5 2 0 o 9 6 0 2 7 4 , 0 9 , 9 5 2 4 , 2 1 2 o 7 5 0 o 9 5 8 2 8 7 , 0 9 , 9 1 2 4 , 3 1 3 0 0 0 O o 9 5 5 9 1 0 0 , 7 9 , 8 8 2 4 , 5 1 3 o 3 3 0 o 9 5 2 1 1 1 6 o 2 9 , 8 0 2 4 , 8 1 3 o 6 7 0 o 9 4 8 2 1 3 0 , 0 9 , 7 2 2 4 , 8 1 4 o 0 0 0 o 9 4 4 1 1 4 3 o l 9 , 6 5 2 5 , 0 1 4 o 5 0 0 , 9 3 7 8 1 5 8 o 5 9 , 5 1 2 4 , 8 1 5 o 0 0 O.o 9306 1 6 8 , 4 9 , 3 9 2 4 . 8 1 5 0 5 0 0 0 9 2 3 2 1 7 4 , 3 9 , 2 2 2 4 , 6 1 6 0 3 3 0 , 9 1 1 5 1 7 8 , 8 8 , 9 7 2 4 . 6 1 7 0 5 0 0 , 8 9 5 2 1 8 2 , 4 8 , 6 2 24 o l 1 9 0 5 0 0 , 8 6 6 1 1 9 1 0 0 8 , 0 2 2 4 . 1 Remarks 8 T E S T E D B Y ? T o J o H , T E S T NOoS 17 D A T E T I M E HRSo V E R T o D I A L I N C H E S PROVo D I A L O o O O O l I N S o B U R E T T E T E M P ° C June 1 3 , 1 9 6 5 2 1 , 4 2 0 0 8 3 7 5 1 9 8 o 6 7 o 5 0 2 4 o 8 2 2 0 5 0 0 o 8 2 0 6 2 0 4 o l 7 o 2 0 2 4 o 8 2 3 0 5 2 0 o 8 0 5 2 2 0 9 o 6 6 0 9 2 2 5 o 0 June 1 4 e 1 9 6 5 2 4 0 7 5 0 o 7 8 7 8 2 1 4 0 4 6 0 6 0 2 4 o 7 2 6 0 0 0 0 0 7 7 0 5 2 2 0 o 2 6 0 3 0 2 5 o 0 3 2 0 5 0 0 0 6 7 4 7 2 6 4 o 2 4 0 9 4 2 4 0 5 3 4 0 0 0 0 0 6 5 3 3 2 7 2 0 1 4 0 6 8 2 4 „ 8 3 5 o 5 0 0 o 6 3 2 4 2 8 3 o 9 4 0 4 1 2 4 o l 3 8 0 0 5 0 o 5 9 5 0 3 0 1 o l 4 o 0 0 2 5 o l 3 9 „ 5 0 0 0 5 7 2 2 3 1 0 o 3 3 0 7 8 2 5 o 0 4 1 o 0 5 0 o 5 5 0 0 3 1 9 o l 3 o 5 5 2 4 0 7 4 2 0 1 3 0 o 5 3 5 1 3 2 4 o 3 3 o 4 0 2 4 0 8 4 3 o 4 5 0 , 5 1 7 0 3 3 4 o 0 3 o 2 2 2 4 o 9 4 5 , 0 3 0 0 4 9 3 8 3 4 4 0 7 3 o 0 1 2 4 , 6 4 6 o 0 0 0 0 4 7 9 4 3 5 1 o 0 2 0 9 1 2 4 0 7 4 7 o 0 O 0 o 4 6 3 8 3 5 7 0 9 2 0 8 0 2 4 , 6 June 1 5 , 1 9 6 5 4 8 o 0 0 0 , 4 4 7 9 3 6 3 0 3 2 o 6 9 2 4 o 0 5 6 0 4 3 0 0 3 2 4 3 4 0 8 o 3 1 , 8 8 25 o 3 5 8 o 0 7 0 , 3 0 1 8 4 1 4 o 7 l o 7 4 . 2 4 o 3 5 9 0 7 3 0 = 2 7 9 7 4 2 3 0 9 1 0 6 2 . . . . . 2 4 , 2 Remarks s 94 T R I A X I A L C O M P R E S S I O N T E S T  ( C O N T I N U E D ) T E S T E D BY8 T o J o H 0 D A T E T I M E HRSo V E R T , D I A L I N C H E S PROVo D I A L O o O O O l I N S o B U R E T T E C M o J T E M P . ° C 0 June 1 5 , 1 9 6 5 6 1 o 9 5 0 , 2 4 6 0 4 3 3 0 2 l o 4 8 2 5 o 0 6 3 o 3 5 0 o 2 2 3 7 4 3 9 o 9 1 0 3 9 2 5 o 0 6 4 o 4 0 0 0 2 0 7 1 4 4 4 o 2 l o 3 0 2 4 o 9 6 5 o 0 5 0 o l 9 7 6 4 4 6 0 3 1 0 2 7 2 5 0 0 6 6 o 5 0 0 o l 7 8 2 4 4 9 0 9 1 0 1 8 ^ 2 5 o 0 6 8 0 1 8 0 o 1 5 5 0 4 5 7 0 1 l o l O 2 4 0 9 6 8 o 8 5 0 0 1 4 4 2 4 6 0 oO I 0 O 6 2 4 o 6 6 9 0 8 7 0 0 1 2 8 5 4 6 3 o 3 l o O O 2 4 o 8 7 0 o 9 7 0 o l l l 7 4 6 7 0 2 0 o 9 7 2 4 0 8 June 1 6 , 1 9 6 5 7 2 o 0 7 0 0 0 9 4 0 4 7 0 o 8 0 o 9 1 2 4 0 8 7 3 o 0 3 0 o 0 7 9 2 4 7 3 o l 0 0 8 8 2 4 o 8 7 3 o 7 5 0 o 0 6 9 1 4 7 3 o 8 0 , 8 4 2 5 o 0 7 3 o 7 5 O 0 I O 8 O 4 7 3 0 8 0 „ 8 4 2 5 0 0 7 5 „ 3 3 0 o 0 8 7 0 4 7 7 o 0 0 o 7 9 2 4 0 6 7 7 o O O 0 0 0 6 2 7 4 8 4 0 7 0 o 7 2 2 4 o 0 7 8 0 8 1 0 0 0 3 3 9 4 9 1 o 7 0 0 6 9 2 3 o 8 A V - 9 0 3 1 O M „ 3 Sheet 3 of 3 TEST N O 0 8 17 Remarks! Sample did not buckle 0 No failure plane visibleo 95 TRIAXIAL BACK-DRAINAGE CHAMBER PRESSURE'GAUGE GAUGE CORRECTION ELEVATION CORRECTION CHAMBER PRESSURE BACK PRESSURE TEST NO, 2 17 TESTED BY % T.J.H. AFTER SHEAR WATER CONTENT = 28„0% WEIGHT DRY SOIL, W WEIGHT WATER, W W • 9 3 , 9 9 GMS 2 6 c 2 9 GMS D A T E TIME H R S . - MIH. ELAPSED T I M E MIN. /ELAPSED V T I M E BURETTE CM.3 VERTlCAt-D lAL 1 NS. TEMR ° C June 16, 1965 06;51 OsOO OoOO 0,69 0,0339 23„8 0204 0025 0sl5 0,50 0*34 0,75 1800 1,00 1834 1,25 2*15 1,50 3804 1,75 0,95 \ 4200 2,00 1,00 \ 6*15 2,50 1,10 9*00 3,00 1,20 12*15 3,50 1,30 16800 4,00 1,40 20*15 4,50 1,50 25*00 5,00 1,59 30*15 5,50 1,69 36*00 6,00 1,78 42 §15 6,50 « , 49 s 00 7.00 1.95 56 §15 7,50 2.02 64 §00 8.00 2,11 81*00 9,00 2,30 121§00 11.00 2,60 144*00 12,00 2,75 169„00 13,00 2,90 211,00 14,52 3,10 245 2 00 15,65 3„25 14*50 3,90 0,1579 25„8 A V - 3,21 CM,3 AFTER BACK-DRAINAGE, WEIGHT OF WATER - W + AV - 29,50 GMS, WATER CONTENT - 31,4% Remarks 2 

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